The Obama administration will be weighing in to urge that Prop 8 be struck down, according to NBC News. Meanwhile, groups across the country are filing briefs against the amendment.

By Chris Geidner

WASHINGTON — Groups from around the country — up to and including the Obama administration, according to one report — are weighing in Thursday in support of California same-sex couples’ rights to marry, with Supreme Court filings in the challenge to the state’s marriage amendment.

NBC’s Pete Williams also has reported Thursday afternoon that the Obama administration will weigh in on the Proposition 8 case, a decision both Obama and Attorney General Eric Holder had not been willing to announce in recent interviews.

Specifics — including the breadth of the administration’s argument — remain unknown, although a brief should be filed later Thursday.

From Williams:

Obama Justice Dept to file Supreme Court amicus brief today opposing Prop 8 in Calif and expressing support for same-sex marriage to resume.

— Pete Williams (@PeteWilliamsNBC) February 28, 2013

The libertarian Cato Institute is pairing up with the left-leaning Constitutional Accountability Center to urge the Supreme Court to strike down both California’s Proposition 8 ban on marriage between same-sex couples and the Defense of Marriage Act’s federal ban on recognizing same-sex couples’ marriages.

The American Sociological Association also weighed in with its own brief, urging the court to strike down DOMA and Proposition 8. The sociological group focused its briefing to the court on opposing the arguments made by supporters of Proposition 8 and DOMA that children fare better with opposite-sex parents.

“The results of our review are clear,” said ASA President Cecilia Ridgeway. “There is no evidence that children with parents in stable same-sex or opposite-sex relationships differ in terms of well-being. Indeed, the greater stability offered by marriage for same-sex as well as opposite-sex parents may be an asset for child well-being.”

The Cato-CAC brief in the Proposition 8 case is being filed Thursday, while the groups’ separate brief in the DOMA case is yet to be filed.

Cato Institute and Constitutional Accountability Center, Opposing Proposition 8 (and DOMA in a later filing): http://www.scribd.com/document_downloads/127819302?extension=pdf&from=embed&source=embed

American Sociological Association, Opposing Proposition 8 and DOMA: http://www.scribd.com/document_downloads/127819899?extension=pdf&from=embed&source=embed