A coalition of labor unions representing federal workers across the United States sued the Trump administration on Friday over its recent order aimed at stripping union rights from more than a million government employees, a move that the lawsuit characterizes as a blatant violation of the First Amendment.

The suit, brought by unions that collectively represent more than 950,000 federal workers, stems from a March 27 order titled “Exclusions From Federal Labor-Management Relations Programs,” in which President Donald Trump cites a provision of a 1978 law to deny collective bargaining rights to certain government workers on national security grounds.

But the unions behind the new lawsuit say the national security justification is a smokescreen to hide the true intent of the order: further eroding workers’ organizing rights.

“Federal employees have had the right to join a union and bargain collectively for decades—through multiple wars, international conflicts, and a global health emergency during President Trump’s first term,” said Everett Kelley, national president of the American Federation of Government Employees. “During all that time, they served the American people with honor and distinction. No one, including President Trump, ever suggested unions were a national security concern.”

“Trump’s newest order to revoke union rights is a clear case of retaliation,” he added. “But I’ve got news for him: We are not going anywhere.”

The lawsuit points specifically to language included in a fact sheet the White House released in conjunction with Trump’s March 27 order. The document claims that “certain federal unions have declared war on President Trump’s agenda,” citing AFGE lawsuits against the administration and legal actions by Veterans Affairs unions.

Shortly after Trump signed the order last week, the administration sued AFGE and many of its local affiliates in federal court in an attempt to cancel dozens of collective bargaining agreements between unions and federal agencies. Reutersnoted that the administration claimed the union contracts are impeding “Trump’s abilities to purge the federal workforce and protect national security.”

“The labor movement stands in solidarity, and we will not let this administration’s union-busting tactics silence us.”

The unions’ new lawsuit states that the “avowedly retaliatory nature” of Trump’s executive order and its “attempt to punish federal unions who engage in politically disfavored speech and petitioning activities and decline to ‘work with’ the president renders it unconstitutional under the First Amendment.”

The lawsuit also notes that billionaire Elon Musk, the richest person in the world and a top Trump lieutenant, has used his social media platform to promote a recent post that attacked several federal workers’ unions by name.

“The president’s unlawful executive order attacking federal unions is not only an attack on a million federal workers but is a direct attack on all workers who seek a collective voice to bargain for a better future,” April Verrett, president of the Service Employees International Union, said in a statement Friday. “This is blatant retaliation against brave workers who dared to exercise their First Amendment rights to criticize this administration’s authoritarian overreach. The labor movement stands in solidarity, and we will not let this administration’s union-busting tactics silence us.”

Randy Erwin, president of the National Federation of Federal Employees (NFFE), called Trump’s order “the most significant assault on collective bargaining rights we have ever seen in the United States” and said it is “clear that this executive order is retaliation for federal unions fighting back against the Trump administration’s attempts to dismantle the civil service.”

“This is yet another direct attack by the President not only on federal employees, but also veterans, working families, and the very fabric of our democracy,” said Erwin. “However, federal workers’ collective bargaining rights are protected by law and President Trump does not have the right to unilaterally eliminate them. NFFE and our allies are confident the rule of law will be upheld, and the critical rights of working people will be protected.”