FICA on SERP Matching Contribution

[Guest mbg]

Employer has a SERP that works on top of 401(k) plan. Participants can make elective deferrals and employer will match using matching criteria from 401(k) plan. Employer withheld FICA on elective deferrals, but forgot to do so on the matching portion. Under Reg. 31.3121(v)(2)-1, it looks like the employer can pay that FICA, plus applicable penalties and interest, before the period of limitations expires and it will relate back to time at which that FICA should have been paid. The Employer has discovered that FICA was not paid on these match amounts, but some of those tax years are past the period of limitations. The regulations say that if FICA is not paid once services are rendered and no SRF applies, then FICA is due when actually or constructively paid. I can't believe that the IRS wouldn't go ahead and hit the employer with a 6656 penalty, but I can't anything covering what happens if FICA on the deferred amount is not paid at the correct time and the employer ultimately withholds when the participant is paid. Any ideas?