26 C.F.R. § 1.215-1T
Q-1 What information is required by the Internal Revenue Service when an alimony or separate maintenance payment is claimed as a deduction by a payor?
A-1 The payor spouse must include on his/her first filed return of tax (Form 1040) for the taxable year in which the payment is made the payee's social security number, which the payee is required to furnish to the payor. For penalties applicable to a payor spouse who fails to include such information on his/her return of tax or to a payee spouse who fails to furnish his/her social security number to the payor spouse, see section 6676.
26 C.F.R. §1.215-1T
98 Stat. 798, 26 U.S.C. 1041(d)(4) ; 98 Stat. 802, 26 U.S.C. 152(e)(2)(A) ; 98 Stat. 800, 26 U.S.C. 215(c) ; 68A Stat. 917, 26 U.S.C. 7805