The federal Defense of Marriage Act (DOMA) was signed into law by President Clinton on September 21, 1996.  DOMA defines "marriage" to consist exclusively as a heterosexual union of a man and a woman.  Further, DOMA directs federal agencies to recognize only opposite-sex marriages for the purposes of enacting any agency programs. 
 
Statutory Language
Among other pertinent provisions, DOMA states: "In determining the meaning of any Act of Congress, or of any ruling, regulation or interpretation of the various administrative bureaus and agencies of the United States, the word ‘marriage’ means only a legal union between one man and one woman as husband and wife, and the word ‘spouse’ refers only to a person of the opposite sex who is a husband or wife." 

State Authority Under DOMA
DOMA also allows each state to determine for itself whether it must recognize same-sex marriages.  In other words, DOMA permits a state that has outlawed same-sex marriage to refuse to recognize a same-sex couple that was married in a state permitting same-sex marriage. 
 
Divergent Viewpoints
Critics of DOMA assert that the law violates the following provisions of the U.S. Constitution, and is therefore unconstitutional:
  • The Full Faith and Credit Clause provides that "full faith and credit shall be given in each state to the public acts, records, and judicial proceedings of every other state."  Critics argue that Congress exceeded its proper authority under the Constitution by enacting DOMA.
  • The Equal Protection Clause guarantees that similarly situated persons will be treated alike.  Critics of DOMA argue that the legislation illegally discriminates against homosexual couples.
  • The Due Process Clause protects certain fundamental rights, including the right to enter into a marriage relationship.  Those opposed to DOMA argue that the law violates this fundamental right by unreasonably restricting the liberty of same-sex couples. 
To the contrary, supporters of DOMA have expressed fear that "liberal" judges will strike down state defense of marriage acts and further erode the "sanctity of marriage."  Those opposed to the legal recognition of same-sex marriages have recommended an amendment to the U.S. Constitution.  If ratified, the "Federal Marriage Amendment" would amend the Constitution to prevent state and federal courts from redefining marriage as anything other than the union of one man and one woman.
 

However, the likelihood of the ratification of such an amendment is unlikely, at best.  In fact, the Constitution has only been amended 27 times since it was adopted in 1787.  Further, in order to amend the Constitution, a two-thirds majority is required in both chambers of Congress (i.e., 290 votes in the House and 67 votes in the Senate), and the amendment must be ratified by at least 38 states.