last sentence of subsection (a)(3)(A), except that 12-month periods beginning before January 1, 2019, shall not be taken into account. . (b) Vesting Section 203(b) of the Employee Retirement Income Security Act of 1974 ( 29 U.S.C. 1053(a) ) is amended by redesignating paragraph (4) as paragraph (5) and by inserting after paragraph (3) the following new paragraph: (4) Part-time employees For purposes of determining whether an employee who is eligible to participate in a qualified cash or deferred arrangement or a salary reduction agreement under a plan solely by reason of section 202(c)(1)(B) has a nonforfeitable right to employer contributions— (A) except as provided in subparagraph (B), each 12-month period for which the employee has at least 500 hours of service shall be treated as a year of service