This document contains final regulations relating to employment tax adjustments and employment tax refund claims. The final regulations modify the process for making interest-free adjustments for both underpayments and overpayments of Federal Insurance Contributions Act (FICA) and Railroad Retirement Tax Act (RRTA) taxes and Federal income tax withholding (ITW) under sections 6205(a) and 6413(a), respectively, of the Internal Revenue Code (Code). These regulations also modify the process for filing claims for refund of overpayments of employment taxes under sections 6402 and 6414. This document contains final regulations relating to the return requirements under section 6011 to reflect the changes to the adjustment and refund processes, and to reflect additional statutory and process updates. This document also contains final regulations under section 6302 to clarify deposit obligations with respect to interest-free adjustments of underpayments and the effect of adjustments and refunds on the deposit schedule of a Form 943 filer.