Five transgender service members filed a lawsuit against President Donald Trump’s apparent decision to reinstate a ban on transgender people serving in the military — a case that could turn on whether official policy can be announced on Twitter.

Lawyers for GLBTQ Legal Advocates & Defenders and the National Center for Lesbian Rights represent plaintiffs who are in the Air Force, the Coast Guard and the Army and served from three years to two decades, including tours in Iraq and Afghanistan. The plaintiffs are not named in the lawsuit filed Wednesday.

The lawsuit’s focus is on Trump’s posts July 26 on Twitter, where the commander in chief wrote that “the United States Government will not accept or allow transgender individuals to serve in any capacity in the U.S. Military.”

The lawsuit claims the White House turned Trump’s tweet into official guidance for the Department of Defense, reversing a policy that allowed the five plaintiffs to serve their country openly.

“This unjustifiable reversal of policy is devastating to these soldiers and harmful to our country,” Jennifer Levi, director of GLAD’s Transgender Rights Project, said in a written statement. “These plaintiffs put their lives on the line every day for all of us. We can’t afford to lose a single one of them.”

But there hasn’t been any official policy announcement or guidance from the Pentagon or elsewhere in the Trump administration. The American Civil Liberties Union says it is likely to challenge any such policy change and has asked the White House to preserve documents for that legal fight — but is still just monitoring the situation.

The case in Washington’s federal district court is Jane Doe 1-5 v. Trump, et al., Docket No. 17-1597.