diff --git a/src/marshmallow/schema.py b/src/marshmallow/schema.py
index b370035d..085c509b 100644
--- a/src/marshmallow/schema.py
+++ b/src/marshmallow/schema.py
@@ -346,7 +346,7 @@ class BaseSchema(base.SchemaABC):
         self.declared_fields = copy.deepcopy(self._declared_fields)
         self.many = many
         self.only = only
-        self.exclude = exclude
+        self.exclude = set(self.opts.exclude) | set(exclude)
         if prefix:
             warnings.warn(
                 'The `prefix` argument is deprecated. Use a post_dump '
@@ -719,19 +719,15 @@ class BaseSchema(base.SchemaABC):
             self.__apply_nested_option('only', self.only, 'intersection')
             # Remove the child field names from the only option.
             self.only = self.set_class(
-                [field.split('.', 1)[0] for field in self.only])
-        excludes = set(self.opts.exclude) | set(self.exclude)
-        if excludes:
-            # Apply the exclude option to nested fields.
-            self.__apply_nested_option('exclude', excludes, 'union')
+                [field.split('.', 1)[0] for field in self.only],
+            )
         if self.exclude:
+            # Apply the exclude option to nested fields.
+            self.__apply_nested_option('exclude', self.exclude, 'union')
             # Remove the parent field names from the exclude option.
             self.exclude = self.set_class(
-                [field for field in self.exclude if '.' not in field])
-        if self.opts.exclude:
-            # Remove the parent field names from the meta exclude option.
-            self.opts.exclude = self.set_class(
-                [field for field in self.opts.exclude if '.' not in field])
+                [field for field in self.exclude if '.' not in field],
+            )
 
     def __apply_nested_option(self, option_name, field_names, set_operation):
         """Apply nested options to nested fields"""
@@ -771,9 +767,7 @@ class BaseSchema(base.SchemaABC):
             field_names = self.set_class(self.declared_fields.keys())
 
         # If "exclude" option or param is specified, remove those fields
-        excludes = set(self.opts.exclude) | set(self.exclude)
-        if excludes:
-            field_names = field_names - excludes
+        field_names -= self.exclude
         ret = self.__filter_fields(field_names, obj, many=many)
         # Set parents
         self.__set_field_attrs(ret)

Defining fields with dot notations in Meta.exclude only works when initialising first time
Demonstration of the issue
``` python
from marshmallow import Schema, fields


class AuthorSchema(Schema):
    first_name = fields.String(required=True)
    last_name = fields.String(required=True)


class BaseSchema(Schema):
    class Meta:
        exclude = ['author.first_name']

    author = fields.Nested(AuthorSchema, required=True)


data = dict(author=dict(first_name='foo', last_name='bar'))
print(BaseSchema().dump(data))
print(BaseSchema().dump(data))
```
results in
```
{'author': {'last_name': 'bar'}}
{'author': {'first_name': 'foo', 'last_name': 'bar'}}
```
diff --git a/tests/test_schema.py b/tests/test_schema.py
index cccc7c91..b9f7534b 100755
--- a/tests/test_schema.py
+++ b/tests/test_schema.py
@@ -938,8 +938,22 @@ def test_meta_nested_exclude():
         blubb = fields.Nested(ChildSchema)
         class Meta:
             exclude = ('blubb.foo',)
-    sch = ParentSchema()
+
     data = dict(bla=1, bli=2, blubb=dict(foo=42, bar=24, baz=242))
+
+    sch = ParentSchema()
+    result = sch.dump(data)
+    assert 'bla' in result.data
+    assert 'blubb' in result.data
+    assert 'bli' in result.data
+    child = result.data['blubb']
+    assert 'foo' not in child
+    assert 'bar' in child
+    assert 'baz' in child
+
+    # Test fields with dot notations in Meta.exclude on multiple instantiations
+    # Regression test for https://github.com/marshmallow-code/marshmallow/issues/1212
+    sch = ParentSchema()
     result = sch.dump(data)
     assert 'bla' in result.data
     assert 'blubb' in result.data

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest pytest-cov pytest-xdist pytest-mock pytest-asyncio
3.9
docs/requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
alabaster==0.7.12
babel==2.17.0
cachetools==5.5.2
certifi==2025.1.31
chardet==5.2.0
charset-normalizer==3.4.1
colorama==0.4.6
coverage==7.8.0
distlib==0.3.9
docutils==0.21.2
entrypoints==0.3
exceptiongroup==1.2.2
execnet==2.1.1
filelock==3.18.0
flake8==3.7.4
idna==3.10
imagesize==1.4.1
iniconfig==2.1.0
Jinja2==3.1.6
MarkupSafe==3.0.2
-e git+https://github.com/marshmallow-code/marshmallow.git@ac9ff95432f929fb0fa2394c29b94d1f804a1504#egg=marshmallow
mccabe==0.6.1
packaging==24.2
platformdirs==4.3.7
pluggy==1.5.0
pycodestyle==2.5.0
pyflakes==2.1.1
Pygments==2.19.1
pyproject-api==1.9.0
pytest==8.3.5
pytest-asyncio==0.26.0
pytest-cov==6.0.0
pytest-mock==3.14.0
pytest-xdist==3.6.1
python-dateutil==2.9.0.post0
pytz==2025.2
requests==2.32.3
simplejson==3.20.1
six==1.17.0
snowballstemmer==2.2.0
Sphinx==1.8.1
sphinx-issues==1.1.0
sphinx-version-warning==1.0.2
sphinxcontrib-serializinghtml==2.0.0
sphinxcontrib-websupport==1.2.4
tomli==2.2.1
tox==4.25.0
typing_extensions==4.13.0
urllib3==2.3.0
virtualenv==20.29.3

name: marshmallow
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - pip=25.0=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - tzdata=2025a=h04d1e81_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - alabaster==0.7.12
      - babel==2.17.0
      - cachetools==5.5.2
      - certifi==2025.1.31
      - chardet==5.2.0
      - charset-normalizer==3.4.1
      - colorama==0.4.6
      - coverage==7.8.0
      - distlib==0.3.9
      - docutils==0.21.2
      - entrypoints==0.3
      - exceptiongroup==1.2.2
      - execnet==2.1.1
      - filelock==3.18.0
      - flake8==3.7.4
      - idna==3.10
      - imagesize==1.4.1
      - iniconfig==2.1.0
      - jinja2==3.1.6
      - markupsafe==3.0.2
      - mccabe==0.6.1
      - packaging==24.2
      - platformdirs==4.3.7
      - pluggy==1.5.0
      - pycodestyle==2.5.0
      - pyflakes==2.1.1
      - pygments==2.19.1
      - pyproject-api==1.9.0
      - pytest==8.3.5
      - pytest-asyncio==0.26.0
      - pytest-cov==6.0.0
      - pytest-mock==3.14.0
      - pytest-xdist==3.6.1
      - python-dateutil==2.9.0.post0
      - pytz==2025.2
      - requests==2.32.3
      - simplejson==3.20.1
      - six==1.17.0
      - snowballstemmer==2.2.0
      - sphinx==1.8.1
      - sphinx-issues==1.1.0
      - sphinx-version-warning==1.0.2
      - sphinxcontrib-serializinghtml==2.0.0
      - sphinxcontrib-websupport==1.2.4
      - tomli==2.2.1
      - tox==4.25.0
      - typing-extensions==4.13.0
      - urllib3==2.3.0
      - virtualenv==20.29.3
prefix: /opt/conda/envs/marshmallow

tests/test_schema.py::test_meta_nested_exclude
tests/test_schema.py::test_serializing_basic_object[UserSchema] tests/test_schema.py::test_serializing_basic_object[UserMetaSchema] tests/test_schema.py::test_serializer_dump tests/test_schema.py::test_dump_returns_dict_of_errors tests/test_schema.py::test_dump_with_strict_mode_raises_error[UserSchema] tests/test_schema.py::test_dump_with_strict_mode_raises_error[UserMetaSchema] tests/test_schema.py::test_dump_resets_errors tests/test_schema.py::test_load_resets_errors tests/test_schema.py::test_dump_resets_error_fields tests/test_schema.py::test_load_resets_error_fields tests/test_schema.py::test_load_resets_error_kwargs tests/test_schema.py::test_errored_fields_do_not_appear_in_output tests/test_schema.py::test_load_many_stores_error_indices tests/test_schema.py::test_dump_many tests/test_schema.py::test_multiple_errors_can_be_stored_for_a_given_index tests/test_schema.py::test_dump_many_stores_error_indices tests/test_schema.py::test_dump_many_doesnt_stores_error_indices_when_index_errors_is_false tests/test_schema.py::test_dump_returns_a_marshalresult tests/test_schema.py::test_dumps_returns_a_marshalresult tests/test_schema.py::test_dumping_single_object_with_collection_schema tests/test_schema.py::test_loading_single_object_with_collection_schema tests/test_schema.py::test_dumps_many tests/test_schema.py::test_load_returns_an_unmarshalresult tests/test_schema.py::test_load_many tests/test_schema.py::test_load_many_invalid_input_type[False] tests/test_schema.py::test_load_many_invalid_input_type[1] tests/test_schema.py::test_load_many_invalid_input_type[1.2] tests/test_schema.py::test_load_many_invalid_input_type[val3] tests/test_schema.py::test_load_many_invalid_input_type[val4] tests/test_schema.py::test_load_many_invalid_input_type[val5] tests/test_schema.py::test_load_many_invalid_input_type[lol] tests/test_schema.py::test_loads_returns_an_unmarshalresult tests/test_schema.py::test_loads_many tests/test_schema.py::test_loads_deserializes_from_json tests/test_schema.py::test_serializing_none tests/test_schema.py::test_default_many_symmetry tests/test_schema.py::test_on_bind_field_hook tests/test_schema.py::test_nested_on_bind_field_hook tests/test_schema.py::TestValidate::test_validate_returns_errors_dict tests/test_schema.py::TestValidate::test_validate_many tests/test_schema.py::TestValidate::test_validate_many_doesnt_store_index_if_index_errors_option_is_false tests/test_schema.py::TestValidate::test_validate_strict tests/test_schema.py::TestValidate::test_validate_required tests/test_schema.py::test_fields_are_not_copies[UserSchema] tests/test_schema.py::test_fields_are_not_copies[UserMetaSchema] tests/test_schema.py::test_dumps_returns_json tests/test_schema.py::test_naive_datetime_field tests/test_schema.py::test_datetime_formatted_field tests/test_schema.py::test_datetime_iso_field tests/test_schema.py::test_tz_datetime_field tests/test_schema.py::test_local_datetime_field tests/test_schema.py::test_class_variable tests/test_schema.py::test_serialize_many[UserSchema] tests/test_schema.py::test_serialize_many[UserMetaSchema] tests/test_schema.py::test_inheriting_schema tests/test_schema.py::test_custom_field tests/test_schema.py::test_url_field tests/test_schema.py::test_relative_url_field tests/test_schema.py::test_stores_invalid_url_error[UserSchema] tests/test_schema.py::test_stores_invalid_url_error[UserMetaSchema] tests/test_schema.py::test_email_field[UserSchema] tests/test_schema.py::test_email_field[UserMetaSchema] tests/test_schema.py::test_stored_invalid_email tests/test_schema.py::test_integer_field tests/test_schema.py::test_as_string tests/test_schema.py::test_extra tests/test_schema.py::test_extra_many tests/test_schema.py::test_method_field[UserSchema] tests/test_schema.py::test_method_field[UserMetaSchema] tests/test_schema.py::test_function_field tests/test_schema.py::test_prefix[UserSchema] tests/test_schema.py::test_prefix[UserMetaSchema] tests/test_schema.py::test_fields_must_be_declared_as_instances tests/test_schema.py::test_serializing_generator[UserSchema] tests/test_schema.py::test_serializing_generator[UserMetaSchema] tests/test_schema.py::test_serializing_empty_list_returns_empty_list tests/test_schema.py::test_serializing_dict tests/test_schema.py::test_serializing_dict_with_meta_fields tests/test_schema.py::test_exclude_in_init[UserSchema] tests/test_schema.py::test_exclude_in_init[UserMetaSchema] tests/test_schema.py::test_only_in_init[UserSchema] tests/test_schema.py::test_only_in_init[UserMetaSchema] tests/test_schema.py::test_invalid_only_param tests/test_schema.py::test_can_serialize_uuid tests/test_schema.py::test_can_serialize_time tests/test_schema.py::test_invalid_time tests/test_schema.py::test_invalid_date tests/test_schema.py::test_invalid_email tests/test_schema.py::test_invalid_url tests/test_schema.py::test_invalid_dict_but_okay tests/test_schema.py::test_custom_json tests/test_schema.py::test_custom_error_message tests/test_schema.py::test_load_errors_with_many tests/test_schema.py::test_error_raised_if_fields_option_is_not_list tests/test_schema.py::test_error_raised_if_additional_option_is_not_list tests/test_schema.py::test_nested_custom_set_in_exclude_reusing_schema tests/test_schema.py::test_nested_only tests/test_schema.py::test_nested_only_inheritance tests/test_schema.py::test_nested_only_empty_inheritance tests/test_schema.py::test_nested_exclude tests/test_schema.py::test_nested_exclude_inheritance tests/test_schema.py::test_nested_only_and_exclude tests/test_schema.py::test_nested_only_then_exclude_inheritance tests/test_schema.py::test_nested_exclude_then_only_inheritance tests/test_schema.py::test_nested_exclude_and_only_inheritance tests/test_schema.py::test_nested_custom_set_not_implementing_getitem tests/test_schema.py::test_deeply_nested_only_and_exclude tests/test_schema.py::TestDeeplyNestedLoadOnly::test_load_only tests/test_schema.py::TestDeeplyNestedLoadOnly::test_dump_only tests/test_schema.py::TestDeeplyNestedListLoadOnly::test_load_only tests/test_schema.py::TestDeeplyNestedListLoadOnly::test_dump_only tests/test_schema.py::test_nested_constructor_only_and_exclude tests/test_schema.py::test_only_and_exclude tests/test_schema.py::test_exclude_invalid_attribute tests/test_schema.py::test_only_with_invalid_attribute tests/test_schema.py::test_only_bounded_by_fields tests/test_schema.py::test_only_empty tests/test_schema.py::test_nested_with_sets tests/test_schema.py::test_meta_serializer_fields tests/test_schema.py::test_meta_fields_mapping tests/test_schema.py::test_meta_field_not_on_obj_raises_attribute_error tests/test_schema.py::test_exclude_fields tests/test_schema.py::test_fields_option_must_be_list_or_tuple tests/test_schema.py::test_exclude_option_must_be_list_or_tuple tests/test_schema.py::test_dateformat_option tests/test_schema.py::test_default_dateformat tests/test_schema.py::test_inherit_meta tests/test_schema.py::test_inherit_meta_override tests/test_schema.py::test_additional tests/test_schema.py::test_cant_set_both_additional_and_fields tests/test_schema.py::test_serializing_none_meta tests/test_schema.py::TestErrorHandler::test_error_handler_decorator_is_deprecated tests/test_schema.py::TestErrorHandler::test_dump_with_custom_error_handler tests/test_schema.py::TestErrorHandler::test_dump_with_custom_error_handler_and_strict tests/test_schema.py::TestErrorHandler::test_load_with_custom_error_handler tests/test_schema.py::TestErrorHandler::test_load_with_custom_error_handler_and_partially_valid_data tests/test_schema.py::TestErrorHandler::test_custom_error_handler_with_validates_decorator tests/test_schema.py::TestErrorHandler::test_custom_error_handler_with_validates_schema_decorator tests/test_schema.py::TestErrorHandler::test_validate_with_custom_error_handler tests/test_schema.py::TestFieldValidation::test_errors_are_cleared_after_loading_collection tests/test_schema.py::TestFieldValidation::test_raises_error_with_list tests/test_schema.py::TestFieldValidation::test_raises_error_with_dict tests/test_schema.py::TestFieldValidation::test_ignored_if_not_in_only tests/test_schema.py::test_schema_repr tests/test_schema.py::TestNestedSchema::test_flat_nested tests/test_schema.py::TestNestedSchema::test_flat_nested_with_dump_to tests/test_schema.py::TestNestedSchema::test_nested_many_with_missing_attribute tests/test_schema.py::TestNestedSchema::test_nested_with_attribute_none tests/test_schema.py::TestNestedSchema::test_flat_nested2 tests/test_schema.py::TestNestedSchema::test_nested_field_does_not_validate_required tests/test_schema.py::TestNestedSchema::test_nested_required_errors_with_load_from tests/test_schema.py::TestNestedSchema::test_nested_none tests/test_schema.py::TestNestedSchema::test_nested tests/test_schema.py::TestNestedSchema::test_nested_many_fields tests/test_schema.py::TestNestedSchema::test_nested_meta_many tests/test_schema.py::TestNestedSchema::test_nested_only tests/test_schema.py::TestNestedSchema::test_exclude tests/test_schema.py::TestNestedSchema::test_list_field tests/test_schema.py::TestNestedSchema::test_nested_load_many tests/test_schema.py::TestNestedSchema::test_nested_errors tests/test_schema.py::TestNestedSchema::test_nested_strict tests/test_schema.py::TestNestedSchema::test_nested_dump_errors tests/test_schema.py::TestNestedSchema::test_nested_dump_strict tests/test_schema.py::TestNestedSchema::test_nested_method_field tests/test_schema.py::TestNestedSchema::test_nested_function_field tests/test_schema.py::TestNestedSchema::test_nested_prefixed_field tests/test_schema.py::TestNestedSchema::test_nested_prefixed_many_field tests/test_schema.py::TestNestedSchema::test_invalid_float_field tests/test_schema.py::TestNestedSchema::test_serializer_meta_with_nested_fields tests/test_schema.py::TestNestedSchema::test_serializer_with_nested_meta_fields tests/test_schema.py::TestNestedSchema::test_nested_fields_must_be_passed_a_serializer tests/test_schema.py::TestNestedSchema::test_invalid_type_passed_to_nested_field tests/test_schema.py::TestNestedSchema::test_all_errors_on_many_nested_field_with_validates_decorator tests/test_schema.py::TestNestedSchema::test_missing_required_nested_field tests/test_schema.py::TestSelfReference::test_nesting_schema_within_itself tests/test_schema.py::TestSelfReference::test_nesting_schema_by_passing_class_name tests/test_schema.py::TestSelfReference::test_nesting_within_itself_meta tests/test_schema.py::TestSelfReference::test_recursive_missing_required_field tests/test_schema.py::TestSelfReference::test_recursive_missing_required_field_one_level_in tests/test_schema.py::TestSelfReference::test_nested_self_with_only_param tests/test_schema.py::TestSelfReference::test_multiple_nested_self_fields tests/test_schema.py::TestSelfReference::test_nested_many tests/test_schema.py::test_serialization_with_required_field tests/test_schema.py::test_deserialization_with_required_field tests/test_schema.py::test_deserialization_with_required_field_and_custom_validator tests/test_schema.py::TestContext::test_context_method tests/test_schema.py::TestContext::test_context_method_function tests/test_schema.py::TestContext::test_function_field_raises_error_when_context_not_available tests/test_schema.py::TestContext::test_fields_context tests/test_schema.py::TestContext::test_nested_fields_inherit_context tests/test_schema.py::TestContext::test_nested_list_fields_inherit_context tests/test_schema.py::test_serializer_can_specify_nested_object_as_attribute tests/test_schema.py::TestFieldInheritance::test_inherit_fields_from_schema_subclass tests/test_schema.py::TestFieldInheritance::test_inherit_fields_from_non_schema_subclass tests/test_schema.py::TestFieldInheritance::test_inheritance_follows_mro tests/test_schema.py::TestAccessor::test_accessor_decorator_is_deprecated tests/test_schema.py::TestAccessor::test_accessor_is_used tests/test_schema.py::TestAccessor::test_accessor_with_many tests/test_schema.py::TestRequiredFields::test_required_string_field_missing tests/test_schema.py::TestRequiredFields::test_required_string_field_failure tests/test_schema.py::TestRequiredFields::test_allow_none_param tests/test_schema.py::TestRequiredFields::test_allow_none_custom_message tests/test_schema.py::TestDefaults::test_missing_inputs_are_excluded_from_dump_output tests/test_schema.py::TestDefaults::test_none_is_serialized_to_none tests/test_schema.py::TestDefaults::test_default_and_value_missing tests/test_schema.py::TestDefaults::test_loading_none tests/test_schema.py::TestDefaults::test_missing_inputs_are_excluded_from_load_output tests/test_schema.py::TestLoadOnly::test_load_only tests/test_schema.py::TestLoadOnly::test_dump_only tests/test_schema.py::TestStrictDefault::test_default tests/test_schema.py::TestStrictDefault::test_meta_true tests/test_schema.py::TestStrictDefault::test_meta_false tests/test_schema.py::TestStrictDefault::test_default_init_true tests/test_schema.py::TestStrictDefault::test_default_init_false tests/test_schema.py::TestStrictDefault::test_meta_true_init_true tests/test_schema.py::TestStrictDefault::test_meta_true_init_false tests/test_schema.py::TestStrictDefault::test_meta_false_init_true tests/test_schema.py::TestStrictDefault::test_meta_false_init_false
src/marshmallow/schema.py
src/marshmallow/schema.py