Gay rights group Human Rights Campaign (HRC) will launch a campaign against law firm King & Spalding's defense of gay marriage ban DOMA on Tuesday in Atlanta.

The campaign will be announced at a press conference at 11AM near the law firm's Atlanta headquarters.

King & Spalding is the private law firm hired by House Speaker John Boehner to defend the Defense of Marriage Act (DOMA) after the Obama administration decided it would no longer defend the statute in court. President Obama has said he believes the law that bans federal recognition of the marriages of gay and lesbian couples is unconstitutional.

Currently, 5 states and the District of Columbia have legalized the institution, and two states – New York and Maryland – recognize those marriages as legal. Gay marriage is legal in ten countries, including nearby Canada.

“The bottom line is that K&S was under no obligation to take this case. They consciously chose to defend a law that discriminates against LGBT Americans, including K&S's LGBT employees and clients. Discrimination, no matter how profitable, is never good business. What's especially appalling and ironic is that K&S ignored its own highly touted commitment to diversity by taking on this unprincipled engagement,” said HRC president Joe Solmonese, referring to King & Spalding's gay-inclusive workplace policies.

The case could add up to $500,000 to the firm's corporate coffers.

HRC's campaign is expected to include ads in mainstream and legal publication that feature the stories of families affected by DOMA, informational letters to the firm's clients, and reconsideration of the firm's Corporate Equality Index score – an HRC ranking of a corporation's support for gay rights.

HRC will be joined by representatives of Georgia Equality, the state's largest gay rights advocate, at Tuesday's event.

The group's executive director, Jeff Graham, told gay weekly The Georgia Voice that he was disappointed with the firm's decision.

“This decision on such a high-profile case … is very disappointing,” Graham said. “This directly affects the future of LGBT families.”