I know part-time employees may not be excluded from participation in a 401(k)plan. Can an employer provide for different match formulas for part-time and full-time employees? Would this be illegal as non-discriminatory on its face, or would it depend on the outcome of the ACP test? (Most of the part-timers are NHCEs.)

In addition to ACP, each level of match would me subject to discrimination testing for current and effective availability under 401(a)(4).

However, if you can pass ACP and 401(a)(4) testing I suppose it would be o.k.

I agree with the above post.

The rules about not being able to exclude part-timers entirely regardless of coverage testing results are based on Code Section 410(a). Nothing in your proposed plan design would violate that Code Section, in my opinion.