Non-ERISA Plan Changing to ERISA Plan - Vesting

[DTH]

A 501©(3) organization established a non-ERISA 403(b) in 2009; only allowed for deferrals. In 2014 they added employer contributions and the plan became subject to ERISA. They added a 4-year graded vesting schedule. There is no predecessor employer

Under ERISA you can exclude vesting service before the establishment of the plan or prior to age 18. Can they exclude the pre-ERISA service? In other words, they want all existing and newly eligible employees to start vesting service in 2014 when the employer contributions were added to the plan. If yes, can you please provide a cite.

Thank You.