It’s two steps forward and one step back for the right-to-work movement—the two steps forward being the new Indiana right-to-work bill, signed into law Feb. 1, and the group in Ohio dedicated to getting a similar amendment on the ballot. But Indiana unions have pushed the movement back a step, asking a federal court to block the new law from being enforced.

The International Union of Operating Engineers Local 150 filed suit in the U.S. District Court in Hammond on Wednesday. Marc Poulos, an attorney representing the union, told the AP that the union will seek a temporary restraining order blocking the law for 10 days while the judge decides its final fate. The union claims that the law violates the Constitution by treating public workers and building and construction workers differently from other employees. The union alleges that public workers aren’t able to opt out of union membership to the same degree as private workers.

Indiana’s right-to-work law is the first to be enacted in the U.S. in more than a decade (the last being in Oklahoma in 2001), and the first-ever in the nation’s union-heavy Rust Belt.