Can anyone tell me what the limitations/requirements are for a part time position, with no benefits, regarding number of hours? I am being told can't exceed 20 hours per week. We don't want to offer our 401K to this part time position.

The financial institution really should consult with legal counsel experienced in ERISA issues, because one mistake can destroy the 401k plan. Here is an article that explains some of the pitfalls when attempting to exclude part time employees.

http://www.nysscpa.org/cpajournal/2007/707/essentials/p60.htm

We were told by our legal counsel no more than 20 hours, however, we do offer 401K to them but not other benefits.