Adding a tab to the login page
You can use hook_menu with type as 'MENU_LOCAL_TASK'. So that your menu path will be like 'user/your_path'.

Ex:

function my_module_menu($items) {
  $items['user/my-path] = array(
    'title' =&gt; 'Some title'
    'page callback =&gt; 'your callback',
    'type' =&gt; MENU_LOCAL_TASK, 
  );
  return $items;
}

If you are using views to print this page, you can set menu as Menu tab in path options.