The rationale for deferring to State law is that domestic relations is "an area that has long been regarded as a virtually exclusive province of the States." Sosna v. Iowa, 419 U.S. 393, 404 (1975); see also Pennoyer v. Neff, 95 U.S. 714, 734-735 (1878); Lee v. Commissioner, 64 T.C. 552 (1975), affd. 550 F.2d 1201 (9th Cir. 1977). See, for example, sec. 143(b).

The rationale for deferring to State law is that domestic relations is “an area that has long been regarded as a virtually exclusive province of the States.” Sosna v. Iowa, 419 U.S. 393, 404 (1975); see also Pennoyer v. Neff, 95 U.S. 714, 734-735 (1878); Lee v. Commissioner, 64 T.C. 552 (1975), affd. 550 F.2d 1201 (9th Cir. 1977). By one estimate, there are more than 40 sections of the Internal Revenue Code under which differing tax consequences may result due to the marital status of the taxpayer.

Our conclusion also properly takes into account the oft-expressed concern that "Congress did not intend that the Commissioner in making tax determinations around marital status, or the courts in passing upon them, should set themselves up as domestic relations tribunals." Estate of Borax v. Commissioner, 349 F.2d 666, 676 (2d Cir. 1965) (Friendly, J., dissenting); see also Lee v. Commissioner, 64 T.C. 552, 557-558 (1975), aff'd, 550 F.2d 1201 (9th Cir. 1977). The parties most keenly interested in the status of Semone and Ziona's marriage--Semone, Ziona, and Hilda--did not challenge the marriage.

We have held that section 6013 limits the benefits of joint filing to married couples. See Lee v. Commissioner, 64 T.C. 552, 560 (1975), affd. 550 F.2d 1201 (9th Cir. 1977); Von Tersch v. Commissioner, 47 T.C. 415, 420-421 (1967). The Commissioner has the right and the obligation to determine whether a man and woman filing a joint return are legally married.

Whether a taxpayer is married for Federal income tax purposes is determined by reference to the laws of the State of the taxpayer's marital domicile. SeeSullivan v. Commissioner, 256 F.2d 664 (4th Cir. 1958), affg. 29 T.C. 71 (1957); Dunn v. Commissioner, 70 T.C. 361, 366 (1978), affd. without published opinion 601 F.2d 599 (7th Cir. 1979); Lee v. Commissioner, 64 T.C. 552, 556-559 (1975), affd. 550 F.2d 1201 (9th Cir. 1977). Petitioners admit that they were not married at the close of 2004.