Attorney General Sam Olens told the Glynn County Bar Association this week that the move by King & Spalding "sets a dangerous precedent and could have a chilling effect on law firms."
He also noted that the same firm represented detainees at the military's Guantanamo Bay complex.
The U.S. House announced in April that it hired King & Spalding partner Paul Clement to defend the ban. The firm filed a motion a week later to drop the case, and Clement immediately resigned to join another firm.
Clement is a former U.S. solicitor general. He plans to continue defending the measure with his new firm.