A referendum allowing Illinois voters to decide if an independent commission should draw the state’s political boundaries was struck down by a judge Wednesday who ruled that it was unconstitutional for the November ballot.

The 37-page written decision by Cook County Circuit Court Judge Diane Larsen was the second setback to advocates of redistricting reform since 2014 when a judge threw out a similar proposal. Both times an attorney linked to Illinois’ top Democratic leaders, including House Speaker Michael Madigan, filed lawsuits claiming the plans weren’t constitutional.

The latest measure by the Independent Map Amendment group proposed an 11-member commission take over drawing legislative boundaries, instead of leaving the process to party leaders. Commission members would be chosen through a complex process involving the state auditor general and potentially Illinois Supreme Court members. Backers, including business and bipartisan political leaders, said they learned from the failed attempt and were better funded. They recently launched a $1 million summer ad campaign.

The group, which claims the once-a-decade redrawing of political districts is too political, vowed Wednesday to file an expedited appeal to the state’s highest court.

“A great deal of care went into crafting an amendment that follows constitutional guidelines while also creating a system that is independent, fair, transparent, and protects the ability of minority communities to elect candidates of their choosing,” Independent Maps chairman Dennis FitzSimons said in a statement. “We believe that the Illinois Supreme Court will side with Illinois voters and not deny citizens the opportunity to vote on this amendment.”

The lawsuit argued the plan didn’t meet the narrow scope that changes to the Legislature be “structural and procedural.” It was filed on behalf of minority business and community groups calling themselves the People’s Map. They claimed the current process protects minority representation, though those arguments weren’t mentioned in court.

People’s Map Chairman John Hooker said Wednesday that the decision was a victory for democracy and minority rights.

“This unconstitutional amendment would put a tremendous amount of authority in the hands of unelected middlemen unaccountable to the taxpayers,” he said in a statement. “Any effort to weaken minority rights harms us all and should be seen as nothing more than a major setback in what has been accomplished for minority rights in Illinois.”

The judge, who called parts of the Independent Map group’s arguments “unavailing,” wrote the proposal didn’t meet constitutional requirements and added extra duties, particularly for the auditor general and Supreme Court members who might be involved in the process.

In court, Independent Map lawyers countered by saying since legislative districts are the “building blocks” of the Legislature, redistricting is by its nature structural and procedural. The group has dismissed the lawsuit was an effort by “entrenched interests.”

The court decision followed a report by The Associated Press that the People’s Map group formed as a political committee last summer but hasn’t disclosed any expenses or donations in state campaign filings despite the expensive legal battle.

Changes to the way Illinois draws political lines every decade could greatly diminish the power of party leaders. Democrats ran the process the last time around because they controlled the state House, Senate and governor’s office.

Top Illinois Republicans criticized the judge’s Wednesday decision.

First-term Gov. Bruce Rauner — the first GOP governor in over a decade — called the ruling a “harsh reminder” that the state needs reform. He pushed a term limits initiative in his gubernatorial bid and backed the 2014 redistricting plan. A judge threw out both.

“Independent Maps has strong support from both Democrats and Republicans,” Rauner said in a statement. “It has strong support from non-partisan good government groups. So this ruling is definitely a setback for the people of Illinois.”

The State Board of Elections had already determined the Independent Map group appeared to have enough valid signatures for the ballot after turning in over 550,000 signatures. Election officials face an Aug. 26 deadline to certify the ballot. An appeal could complicate the timing.