Hi guys,
I started work in Jan -08 on OPT. In Oct 2008, my H1-B was approved. My employer hasn't taken out any SS or Medicare taxes to date. I just caught this mistake recently. What are my options?
Thanks

Ask your employer to withhold SS tax and Medicare on your payments during H-1B.

Agreed. However, the employer May want to collect the back withholdings that should have started on 1 October 2008.

In my opinion, he has NO LEGAL STANDING to do so. He does have standing to collect from 1 January 2009, however.

It is possible that the employer will start withholding the SS and Medicare taxes and NOT ask for the back payments, hoping the IRS will not notice. Their failure to properly withhold these taxes starting on 1 October 2008 will subject to some rather large fines, fines which THEY must pay. You cannot be held liable for the payment of the fines.

If the employer chooses to avoid paying the back-due taxes, you have little leverage on this matter, because the employer can dismiss you if you cause too much of a problem. I recommend that you negotiate the best deal you can in order to hold onto your job.