The IRS announced two special procedures for employers to correct overpayments of employment taxes made in 2013. The first procedure allows employers to use the fourth quarter 2013 Form 941, Employer’s Quarterly Federal Tax Return, to correct the overpayment of FICA and federal income tax withholdings made during the first three quarters of 2013. The second procedure allows employers to file one Form 941-X, Adjusted Employer’s Quarterly Federal Tax Return or Claim for Refund, for the fourth quarter of 2013 to correct the overpayment of FICA taxes during all quarters of 2013. For the overpayment of FICA taxes in years prior to 2013, employers may make a claim or adjustment for all four calendar quarters of a specific year by filing one Form 941-X. The employer can file a Form 941-X filed for the fourth quarter of a specific year if the year is still open under the statute of limitations on refunds and, in the case of adjustments, the statute of limitations will not expire within 90 days of filing the adjusted return.
IRS Notice 2013-61 can be found here.