US Supreme Court justices have indicated interest in striking down a law that denies federal benefits to legally married same-sex couples.
Justice Anthony Kennedy, a potential swing vote, warned of "risks" that the Defense of Marriage Act (Doma) could infringe upon the traditional role of the states in defining marriage.
The 1996 US law denies married same-sex couples access to federal benefits.
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Several justices raised concerns about the law, indicating there could be a narrow majority to strike it down.
Justice Ruth Bader Ginsburg stressed how important federal recognition is to any person who is legally married. "It affects every area of life," she said.
The law is the focus of a second day of oral arguments before the high court as it tackles the gay marriage issue.
Conservatives also criticised the decision by President Barack Obama to abandon the legal defense of Doma and called into question his willingness to defend other laws passed by Congress and challenged in court, several conservative justices said. "It's very troubling," Justice Kennedy said.
While the criticisms may not affect how the justices eventually rule on whether the 1996 law violates U. equal protection rights, it showed frustration with how Mr Obama has walked a difficult political line on gay marriage.
Mr Obama and his attorney general, Eric Holder, said in February 2011 they would cease defending the law because they believed it to be invalid under the US Constitution.
In the place of the US justice department, Republican lawmakers have stepped in to argue for the law.
Chief Justice John Roberts pressed government lawyer Sri Srinivasan on how the government will now decide which laws to defend. "What is your test?" Justice Roberts asked.
Mr Srinivasan said he could not give the justices a "black or white" test. On the marriage law, the final decision rested with Mr Obama, not with an official at a lower level, he said.
Reuters