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President Donald Trump’s ban on transgender military service has been the target of a growing number of lawsuits since he first announced the policy via tweet in late July. But now the controversial move has drawn the attention of the world’s highest-grossing law firm.

Latham & Watkins represents the LGBT civil rights group Equality California and several transgender members of the military in a federal lawsuit filed Tuesday in California challenging the constitutionality of Trump’s Aug. 25 directive to the heads of the military.

The lawsuit—which lists the president, Defense Secretary Jim Mattis, the chairman of the Joint Chiefs of Staff and the secretaries of each branch of the armed forces as defendants—seeks to “ensure that all qualified Americans have an equal opportunity to serve in the United States military, that transgender individuals are free from arbitrary and invidious discrimination, and that the constitutional rights of transgender individuals to autonomy, privacy, and freedom of expression are respected and protected.”

Just over a month ago, Trump kicked off a firestorm when he tweeted “after consultation” with “generals and military experts,” the government “will not accept or allow transgender individuals to serve in any capacity in the U.S. military.”

Trump cited health care costs associated with gender reassignment surgery as the reason for the ban.

“Military policy must be based on military concerns, not politics,” said Shannon Minter, the legal director of the National Center for Lesbian Rights, in a statement released by released by Equality California on Tuesday. NCLR worked with Equality California and Latham & Watkins in preparing the case.

“As the military itself concluded, transgender people who qualify for military service are just as capable of serving our country as others. The president’s new policy is an assault on dedicated service members who deserve nothing but our gratitude and respect, and it will undermine our national security.”

This newest legal challenge of the ban was filed on the heels of a similar federal lawsuit was filed in the U.S. District Court for the District of Columbia.

In that case, five transgender service members including veterans of Iraq and Afghanistan claimed the ban violated the equal protections clause of the Constitution.

In June 2016, President Barack Obama and Defense Secretary Ash Carter announced a change in standing policy for transgender people serving in the armed forces. The announcement included a one-year plan to allow transgender people to enlist and immediately made it so service members could no longer be discharged for being transgender. Last month, Mattis delayed the July 1 deadline to begin enlisting transgender people by six months.

In the wake of Trump’s tweet, several groups, including the American Civil Liberties Union, were poised to take legal action. In a written statement senior staff attorney Joshua Block implored any service members affected by the announcement to “please get in touch with us, because we want to hear from you.”

Tuesday’s lawsuit also pointed out the logistical nightmare that would occur by discharging and attempting to replace active-duty transgender service members en masse, citing research from the Naval Postgraduate School published by the Palm Center along with a study conducted by the RAND Corp.

The Navy’s report “concludes that the ‘financial cost of fully implementing President Trump’s ban on transgender servicemembers would be $960 million,’ assuming the military acted to expel the estimated 12,800 transgender servicemembers and needed to replace them,” the complaint said.

“Even assuming the military acted to expel and replace only 1,320 transgender servicemembers, which was the RAND Report’s lowest estimate of the total number of active transgender servicemembers,” the lawsuit continued, “the Palm Center Report indicates the financial cost of fully implementing President Trump’s ban would still be at least $99 million.”