A law firm hired by the House of Representatives Bipartisan Legal Advisory Group to defend the Defense of Marriage Act (DOMA) has filed a motion to withdraw from serving as its counsel.

King and Spalding represented the group and last week, House Speaker John Boehner, R-Ohio, announced that King and Spalding partner Paul Clement, a former Bush solicitor general, would take the lead.

"Today the firm filed a motion to withdraw from its engagement to represent the Bipartisan Legal Advisory Group of the House of Representatives on the constitutional issues regarding Section III of the 1996 Defense of Marriage Act," King and Spalding chairman Robert D. Hayes Jr. said in a statement. "Last week we worked diligently through the process required for withdrawal."

Soon after the firm issued that statement, Clement, announced he was leaving the firm and joining Bancroft PLLC. In that new role, he will still serve as counsel to the House Bipartisan Legal Advisory Group.

"My resignation is, of course, prompted by the firm's decision to withdraw as counsel for the Bipartisan Legal Advisory Group of the United States House of Representatives in defense of Section III of the Defense of Marriage Act," Clement said in a resignation letter obtained by Fox News. "To be clear, I take this step not because of strongly held views about this statute...""Instead, I resign out of the firmly-held belief that a representation should not be abandoned because the client's legal position is extremely unpopular in certain quarters. Defending unpopular positions is what lawyers do."

King and Spalding had come under fire from gay and lesbian rights advocates for signing on to represent the House in defending the law.

DOMA, the 1996 law that defines marriage as being between a man and woman, has come under fire of late and the Obama Justice Department has stopped defending it, citing concerns about its constitutionality. When the Obama administration announced its intention to stop defending the law, Boehner convened the legal advisory group-and hired King and Spalding-to step in to defend it against constitutional challenges.

In filing the motion to withdraw, King and Spalding's chairman took the blame, saying the firm should have looked deeper into the issue before committing to defend DOMA.

"In reviewing this assignment further, I determined that the process used for vetting this engagement was inadequate," Hayes said. Ultimately I am responsible for any mistakes that occurred and apologize for the challenges this may have created."

Boehner expressed disappointment in King and Spalding's decision to walk away from defending DOMA, but applauded Clement's move to continue representing the group..

"The Speaker is disappointed in the firm's decision and its careless disregard for its responsibilities to the House in this constitutional matter," Boehner spokesman Brendan Buck said in an email to Fox News. "At the same time, Mr. Clement has demonstrated legal integrity, and we are grateful for his decision to continue representing the House. This move will ensure the constitutionality of this law is appropriately determined by the courts, rather than by the President unilaterally."