Under a 401(k) plan with no age or service requirements for eligibility, once an employee is hired is that individual automatically considered a participant, or would that person need to make a salary reduction election to become a participant?

The answer seems like it would be the former. I'm just reading over some of the requirements for a qualified CODA and wanted to make sure I wasn't excluding anyone from possible QNEC's.

Thanks again guys.

The answer is indeed the former. Satisfying eligiblity (and passing an entry date) is all that is required to become a participant.

You didn't mention entry dates, so you'd better check your doc, if you haven't already.