Lambda Legal, an LGBT rights group, is gearing up to sue the Trump administration over President Trump's proposal to ban transgender people from serving in the military.

Trump announced via Twitter last week that he would revive a policy barring transgender people from serving openly in the military. But that announcement came with no formal guidance and the Pentagon said it would continue to allow transgender people to serve until it received new direction from the White House.

A report published Friday by the Los Angeles Blade, however, indicated that the White House had approved guidance for implementing the ban, which Lambda legal called a "mean-spirited and discriminatory attack" on the LGBT community.

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"Lambda Legal has a long history of fighting for LGBT service members and, teaming up with OutServe-SLDN, we’re more than ready to fight like hell again," Sasha Buchert, a staff attorney for the group, wrote on its website. "See you in court, President Trump."

News of Trump's intent to revive the ban, which was lifted last year under the Obama administration, was met with praise by social conservatives and widely condemned by LGBT activists and allies.

Democrats and some Republican lawmakers also slammed the policy, including Sen. John McCain John Sidney McCainMcSally says current Senate should vote on Trump nominee Say what you will about the presidential candidates, as long as it isn't 'They're too old' The electoral reality that the media ignores MORE (R-Ariz.), the chairman of the powerful Senate Armed Services Committee.

"Any American who meets current medical and readiness standards should be allowed to continue serving,” he said.