; or (ii) is a plan described in section 210(a) that covers fewer than 1,000 participants, but only if no single employer in the plan has 100 or more participants covered by the plan. . (e) Effective date (1) In general The amendments made by this section shall apply to plan years beginning after December 31, 2020. (2) Rule of construction Nothing in the amendments made by subsection (a) shall be construed as limiting the authority of the Secretary of the Treasury or the Secretary's delegate (determined without regard to such amendment) to provide for the proper treatment of a failure to meet any requirement applicable under the Internal Revenue Code of 1986 with respect to one employer (and its employees) in a multiple employer plan. 3. Modification of PBGC premiums for CSEC plans (a) Flat rate premium Subparagraph (A) of section 4006(a)(3) of the Employee Retirement Income Security Act of 1974 ( 29 U.S.C. 1306(a)(3) ) is amended— (1) in clause (i), by striking plan, and inserting plan other than a CSEC plan (as defined in section 210(f)(1)) ; (2) in clause (v), by striking or at the end; (3) in clause (vi), by striking the period at the end and inserting , or