26 CFR 1.410(a)-6 - Amendment of break in service rules; Transition period.
(a)In general. Under section 1017(f) (1) of the Employee retirement Income Security Act of 1974, a plan is not a qualified plan (and a trust forming a part of such plan is not a qualified trust) if the rules of the plan relating to breaks in service are amended, and -
(1) Such amendment is effective after January 1, 1974, and before the date on which section 410 becomes applicable to the plan, and
(b)Break in service rules. For purposes of paragraph (a), the term “break in service rules” means the rules provided by a plan relating to circumstances under which a period of an employee's service or plan participation is disregarded for purposes of determining his rights to participate in the plan, if under such rules such service is disregarded by reason of the employee's failure to complete a required period of service within a specified period of time.