hours of service
(5) Year of service (A) General rule For purposes of this subsection, except as provided in subparagraph (C), the term “year of service” means a calendar year, plan year, or other 12-consecutive month period designated by the plan (and not prohibited under regulations prescribed by the Secretary of Labor) during which the participant has completed 1,000 hours of service. (B) Hours of service For purposes of this subsection, the term “hours of service” has the meaning provided by section 410(a)(3)(C). (C) Seasonal industries In the case of any seasonal industry where the customary period of employment is less than 1,000 hours during a calendar year, the term “year of service” shall be such period as may be determined under regulations prescribed by the Secretary of Labor. (D) Maritime industries For purposes of this subsection, in the case of any maritime industry, 125 days of service shall be treated as 1,000 hours of service. The Secretary of Labor may prescribe regulations to carry out the purposes of this subparagraph.