Gay marriage foes are mobilizing against Supreme Court nominee Elena Kagan.

President Barrack Obama announced Monday that Kagan was his choice to replace outgoing Justice Paul Stevens.

The National Organization for Marriage (NOM), the nation's most vociferous opponent of gay marriage, wasted no time in labeling Kagan a “radical” nominee who would “impose gay marriage in all 50 states.”

NOM alleges that Kagan, who as solicitor general defended the Defense of Marriage Act (DOMA), the 1996 law that defines marriage as a heterosexual union for federal agencies, purposefully filed a weak legal defense to DOMA.

“The brief that Elena Kagan filed as solicitor general on DOMA explicitly and gratuitously rejected the key legal defense for marriage as the union of husband and wife – that such unions uniquely protect children by encouraging responsible procreation,” Brain Brown, president of NOM, said in a statement.

“Kagan's brief was designed to, and in fact will, undermine the legal defense of marriage currently before the federal courts,” he added, referring to three legal challenges currently wending their way through the federal court system.

One of the suits challenges the constitutionality of California's gay marriage ban, Proposition 8. The ban, narrowly approved by voters in 2008, trumped a state Supreme Court ruling that legalized gay marriage in the state. A federal judge is expected to hear closing arguments in June.

The other two cases challenge DOMA. But neither is looking to overturn section 2 of the law, which allows states to ignore legal gay marriages performed in other states. Instead, the lawsuits narrowly focus on federal benefits such as income tax benefits and Social Security payments being denied to gay and lesbian couples legally married in the state of Massachusetts.

All three cases are expected to reach the Supreme Court.

Other groups opposed to gay rights expressed their opposition to Kagan during her 2009 confirmation as solicitor general.

In a letter written by anti-gay rights stalwarts the American Family Association and Focus on the Family, the groups warned senators that Kagan's “extreme rhetoric makes it highly likely that she also favors same-sex marriage.”

Kagan's support for repeal of “Don't Ask, Don't Tell,” the 1993 law that outlaws gay troops from serving openly, has also angered social conservatives who want the military policy to remain.

The 50-year-old Kagan has also been the subject of a whisper campaign that she is a lesbian, long considered a definite deal-breaker for confirmation.

In a CBS News item, blogger Ben Domenech, a former Bush administration aide, wrote if picked Kagan would be the “first openly gay justice.” Saying he was “applying old stereotypes to single women with successful careers, the White House chided Domenech, who apologized for the posting, but refused to retract the allegation.