Tax question

 Suppose a person was paid a signing bonus to join a new company in 2006, but such signing bonus was subject to repayment if the person left within two years.  The repayment was prorated based on the number of months the person stayed at the job. 

So, for example if the signing bonus was $24,000 paid in 2006, and the person left employment after 18 months, he would owe $6,000 back upon leaving.

When the $24,000 was paid in 2006, that would have been treated as wages and FICA and income tax withholding would have been taken out.

What happens in 2007 when he has to repay the $6,000, does he make some type of claim for overwithheld FICA in 2006?  I understand he can take a deduction on Schedule A for the amount of the repayment, but I'm not sure what is done, if anything, with FICA.

If I'm not mistaken, you need to get it back from the employer, not the IRS.