The National Treasury Employees Union has filed a lawsuit that seeks to block President Donald Trump’s March 27 executive order revoking the collective bargaining rights of hundreds of thousands of unionized government employees.

The lawsuit contends that the March 27 order, which applies to workers in over a dozen federal agencies, violates those workers’ rights and the U.S. Constitution. The executive order directs the agencies to stop payroll deductions for union dues.

If federal employees lose union representation, the Trump administration could more easily change working conditions and fire or discipline workers. The National Treasury Employees Union says the president wants to punish unions for challenging his efforts to cut the workforce.

The executive order affects 75% of federal workers who are currently represented by unions, including workers in the Justice, State, Defense, Treasury, Veterans Affairs and Health and Human Services departments.

Trump said in his order that the revocation of collective bargaining rights was necessary to safeguard national security, but none of the affected agencies is primarily responsible for intelligence or national security work, according to the union lawsuit.