Missouri labor unions have taken the state to court over a new law championed by Republican lawmakers that makes it easier to fire state workers, saying the changes infringe on collective bargaining rights enshrined in the state constitution.

“We are fighting this unjust and illegal attack on the rights of our members every step of the way, and we are confident that justice will prevail,” said Danny Homan, the president of the American Federation of State, County and Municipal Employees Council 61.

The measure designated an estimated 25,000 state workers — nearly half the state workforce — as “at-will” employees, subjecting them to termination for any reason, or even no reason. The unions’ lawsuit says the changes to state employees’ work rules and conditions ignored contractual rights agreed to in contracts still in effect.

Missouri’s former governor, Eric Greitens, signed the law the day before resigning amid allegations of sexual assault and looming impeachment.