Republicans in Michigan filed a second federal lawsuit Thursday challenging a newly created independent redistricting commission, arguing that the panel’s restrictions limiting the partisan affiliation of commissioners violate the U.S. Constitution.

Michigan voters overwhelmingly approved a constitutional amendment last fall that gives a 13-person commission the power to draw congressional and state legislative districts. The panel has four Republicans, four Democrats and five members unaffiliated with either party. In an effort to limit partisanship on the panel, there are restrictions on who can serve. For example, a commissioner can’t have run or held elected office within the last six years or served as an officer or member of a political party. A commissioner also can’t be a parent, child or spouse of anyone who would be ineligible to sit on the panel.

In the new lawsuit, filed in Grand Rapids, the state Republican Party, its chairwoman and four other people affiliated with the GOP say those restrictions violate the First and 14th Amendments and infringe on their guarantee of freedom of speech and freedom of association.

“The proposal usurps the role of political parties in selecting their nominees for partisan public office, and in the case of the Michigan Republican Party, places that responsibility instead in the hands of a highly partisan elected official of the opposite political party,” lawyers wrote in the filing. “At the same time, the proposal penalizes applicants who affiliate with one of the two major political parties by allocating a minority of seats on the commission to each of those pools of applicants.”

The U.S. Supreme Court handed Republicans a significant victory in June when it said federal courts can’t strike down gerrymandered districts on partisan grounds. In his opinion for a five-justice majority, Chief Justice John Roberts wrote that states could still act on their own to restrict excessive partisan gerrymandering. Roberts specifically pointed to Michigan as an example where this was possible.