Clint Eastwood has added his name to an amicus brief to the Supreme Court signed by more than 100 conservatives and Republicans backing same-sex marriage.

Breitbart News first reported that Eastwood had signed the brief, to be filed today. The brief is asking the Supreme Court to uphold lower court decisions that ruled that California’s Proposition 8 is constitutional. Earlier in the week, there were reports that dozens of prominent Republicans and strategists would sign it, including Meg Whitman, who had previously supported Proposition 8. Others signing the brief include Paul Wolfowitz, Romney for President campaign manager Beth Myers and former Utah Gov. Jon Huntsman.

A spokesman for the American Foundation for Equal Rights confirmed that Eastwood had signed the brief.

Eastwood has already publicly declared his support for same-sex marriage, when he was asked about it during the publicity tour for his 2011 movie “J. Edgar.” The screenwriter of that film, Dustin Lance Black, is on the board of the American Foundation for Equal Rights, the organization that is bringing the legal challenge to California’s ban on same-sex marriage.

A group of 200 companies, including Apple and the Walt Disney Co., signed a brief asking the high court to overturn much of the Defense of Marriage Act, which restricts federal benefits to same-sex couples and requires that only a marriage between a man and a woman be recognized. More than 100 businesses in California also were to sign a brief in opposition to Prop 8. A central argument is that the maze of marriage laws in different states places additional burdens on companies as they determine such things as tax withholding and offering of health benefits.

Today is the deadline for amicus briefs opposing Prop 8. A big question is whether the White House will weigh in on the case. It already has announced that is will not defend the Defense of Marriage Act.

The court will hear oral arguments on the Prop 8 case on March 26, and on the DOMA case on March 27.

Update: The Obama administration will file a brief urging the overturning of Proposition 8, NBC News reports. This is big news, as it represents a shift in Obama’s position in support of same-sex marriage but that the states should be left to decide.

Rick Jacobs of the Courage Campaign put out this statement: “We applaud
President Obama for standing-up for millions of Californians who simply want to
marry the person they love. The two Supreme Court cases this summer will be a
watershed moment for equality and President Obama has put his Administration
squarely on the right side of history. Last November,  voters from Maine
to Washington stood up for equality. Now it’s time for the Supreme Court to
catch up with the American public. Discrimination and hatred have no place in a
country founded on the principles of liberty, justice and equality.”

Second update: Also signing the conservatives’ brief, which is led by former Republican National Committee chairman Ken Mehlman, are two former FCC chairmen, Kevin Martin and Michael Powell. Martin is significant because the perception during his tenure was that he was a social conservative, as he pressed forward with measures to curb broadcast indecency, and he once even was rumored to be eyeing a run for governor of North Carolina. Powell’s father, former Secretary of State Colin Powell, already came out in support of same-sex marriage. The younger Powell serves as the head of the National Cable and Telecommunications Assn.

One more note: Eastwood’s entry in the court brief lists him not just as filmmaker, but as the former mayor of Carmel, Calif.

An excerpt from the brief: “Same-sex couples, just like couples composed of a man and a woman,
benefit from the security and bilateral loyalty conferred by civil marriage. There is no reason to believe that the salutary effects of civil marriage arise to any lesser degree when two women or two men lawfully marry each other than when a man and a woman marry.”