Democrats in the Michigan Senate passed a bill Tuesday that would repeal the states decade-old right-to-work law, setting up a potentially historic legislative victory for the states labor unions.

Lawmakers in the Democratic-controlled House already passed similar legislation earlier this month. The Detroit News reported that the House would have to take up the Senate version again before it can head to the desk of Gov. Gretchen Whitmer, a Democrat.

The bill passed the Senate 20-17 along party lines.

Right-to-work laws forbid unions and employers from entering into agreements that require every worker under the contract to pay fees to the union. The laws can weaken unions by allowing workers to opt out of paying dues while still enjoying the benefits of representation.

Anti-union conservatives have managed to muscle right-to-work laws through several statehouses in recent years, so that the laws are now on the books in 27 states. Michigan passed its law under then-Gov. Rick Snyder, a Republican, in 2012, and implemented it the following year. The move was a significant blow to the labor movement in part because Michigan, as the cradle of the U.S. auto industry, has historically been a strong union state.

It is highly unusual for a state to repeal such a law once its in effect. In fact, the Economic Policy Institute, a left-leaning think tank, says Michigan would be the first state to do so in 60 years if Whitmer signs the legislation. (In 2018, Missouri voters passed a referendum blocking a right-to-work law that had recently been passed by GOP lawmakers.)

Union supporters had gathered in the capital of Lansing on Tuesday, urging lawmakers to press ahead with the repeal. Ditching the right-to-work law had become a progressive rallying cry once Democrats took full control of state government after the November election.

This is a developing story and will be updated.