Safe Harbor NonElective Mid-Year Under SECURE Act

[PensionPro]

A non safe harbor 401(k) plan with 3 months eligibility wants to add the 3% SH nonelective by December 1 as provided by the SECURE Act.  However, they only want to add this feature for not otherwise excludible employees who are age 21 and have a YOS.  They will test the otherwise excludible group under ADP/ACP.  Can they do this?  I could not find anything that prohibits it.  Thanks for any comments, insights, and citations.

[Bill Presson]

You can do it, but if the plan is top heavy, the otherwise excludable group will likely have to get a top heavy minimum contribution.