Where can I find info regarding the one time irrevocable election not to participate? We have a takeover plan which originally was profit sharing only. Dr Y participated. Dr X made irrecovable election not to participate. Amended to add 401(k) in 2000. Drs X and Y say they made an irrevocable election "not to participate" at that time. Prior TPA did not include X or Y on ADP test nor did they (when other owners did) receive the 3% Top heavy minimum. They can't do that -- can they? Once some time period has elapse, I thought Dr Y could not make such an election. Also, seems like there was some issue about owners not being able to use this election for 401(k) plans --
Plan Doc says -- participant may "waive Participation in the Plan for any Plan Year. A waiver will be permitted only if it does not adversely affect the Plan's tax qualified status."
Could Dr Y have made an irrevocable election years after the original PSP effective date? Are X and Y included in the ADP test?

1.401(k)-1(a)(3)(iv)
A one time elcetion is not treated as a deferral election

A cash or deferred election does NOT include a one time irrevocable election upon an employee's COMMENCEMENT of employment or upon the employee's first becoming eligible under ANY plan

1.401(k)-1(g)(4)(ii) adds that a person making a one time election is not an eligible employee.

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If you are not eligible, then you are not on the ADP test. Though this could cause coverage to fail since this exclusion is not due to age / service.
if you were ever in a plan then you can not make the 'one time election'. you can elect not to defer, but that is not the same thing.