A federal court has granted attorneys with a Christian legal firm a motion to intervene in a lawsuit that challenges Proposition 8 and the federal Defense of Marriage Act.

The U.S. District Court for the Central District of California, Southern Division, filed the order granting the motion on Wednesday. Alliance Defense Fund attorneys will intervene on behalf of ProtectMarriage.com, the main proponents of Proposition 8 – California's constitutional amendment defining marriage as between a man and a woman.

"The people of California want marriage to remain as the union between one man and one woman; they made their voice clear last November at the polls," said ADF Senior Legal Counsel Brian Raum in a statement released Friday. "Yet this lawsuit begs the court to nullify the voices of more than 7 million California voters, as well as put an end to the federal law on marriage."

Arthur Smelt and Christopher Hammer, who have been in a committed relationship for over 10 years, filed suit against the state of California and the United States of America in December 2008, claiming that both Proposition 8 and the federal Defense of Marriage Act violate the U.S. constitution, specifically the Equal Protection Clause.

The 1996 federal Defense of Marriage Act (DOMA), enacted under the Clinton administration, defines marriage as a legal union between one man and one woman for purposes of all federal laws, and provides that states need not recognize same-sex marriages from another state.

Smelt and Hammer obtained a marriage license in California in July 2008, months after the state Supreme Court legalized same-sex marriage in May. The court ruling was overturned when 52 percent of voters voted in November to pass Proposition 8. The decision on whether to nullify or preserve the 18,000 same-sex marriages performed between May and November is pending in the state high court.

The plaintiffs have asked the court to eliminate California's amendment banning same-sex marriage and to issue a broad injunction "mandating the use of gender-neutral terms in all legislation affecting marriage."

Smelt v. United States of America is the second legal challenge to Proposition 8.

Arguments for the first challenge (Strauss v. Horton) were heard earlier this year by the California Supreme Court. Opponents of Proposition 8 had argued that the measure violates the inalienable right to marry and was an invalid constitutional "revision" rather than just an "amendment."

A decision by the state high court is expected before June 3.

Arguments for Smelt v. United States of America, meanwhile, are not expected to be heard until fall of 2009, said Jim Campbell of ADF.