Paul Clement, the attorney hired to defend in court the Defense of Marriage Act (DOMA), has resigned from the Atlanta-based law firm King & Spalding after the firm announced on Monday it was withdrawing from the case.

House Speaker John Boehner appointed and led a committee that instructed House counsel to defend the law in court after the Obama administration announced it would no longer do so. The president has said he believes the law that bans federal recognition of the marriages of gay and lesbian couples is unconstitutional.

Gay rights groups had begun to mobilize a campaign against the firm, which stood to gain as much $500,000 from the case. The Human Rights Campaign (HRC), the nation's largest gay rights advocate, had scheduled a press conference for Tuesday near the firm's Atlanta-based headquarters to discuss the campaign.

Almost immediately after Chairman Robert D. Hays, Jr. announced the reversal on Monday, the legal blog Above the Law posted Clement's blistering letter of resignation, in which he chided his former employer for “abandoning” his client.

“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,” Clement wrote. “Defending unpopular positions is what lawyers do.”

“I have every good wish for the firm, but I intend to follow Judge [Griffin] Bell's guidance and see this representation through with my new colleagues at Bancroft PLLC.”

Bancroft PLLC is the Washington-based law firm founded by Viet D. Dinh, a former assistant attorney general and law professor at Georgetown University Law Center.