LANSING, MI — A federal lawsuit claiming Michigan’s political districts give Republicans an unfair advantage is coming, says Attorney Mark Brewer.

“We are planning a lawsuit claiming, with good evidence, that the House and Senate and Congressional redistricting plans are partisan gerrymandered,” said Brewer, who used to chair the Michigan Democratic Party but said he was not working with them on this issue.

Michigan’s new districts were drafted by Republicans and signed into law by Gov. Rick Snyder in 2011. Democrats, led by Brewer at the time, claimed the districts were unfair but never challenged them in court.

Bill Ballenger, of capitol newsletter The Ballenger Report, said that was with good reason.

“It was an absolute masterpiece… the Democrats realized it was futile to contest this, until now,” he said.

What changed everything was one state: Wisconsin. A federal court there decided Wisconsin Republicans had unfairly gerrymandered the districts. Perhaps chief among the factors that swayed judges was the introduction of a mathematical formula that measured something called the “efficiency gap.”

What it does is look at “wasted votes” — those cast for a candidate who does not ultimately win, as well as those cast for a winning candidate above and beyond what that candidate needed to win the seats. When the difference between wasted votes for the parties is divided by the total number of votes, the result is that efficiency gap.

In completely fair districts, the result would be zero. A positive number for one party indicates that party had an advantage. The larger the number, the bigger the advantage.

The Wisconsin case, which resulted in a split decision, will likely go before the U.S. Supreme Court.

If the ruling is affirmed there, Ballenger said, “I think Michigan would be Exhibit A.”

Brewer has been working with the attorneys from the Wisconsin case, and sees opportunity in Michigan.

“The Wisconsin case changes the law dramatically. It establishes now a way forward for plaintiffs to prove a partisan gerrymander that didn’t exist before,” Brewer said.

Ballenger said due to political circumstance both parties had some level of input on redistricting for years in Michigan. But 2001 the first time since 1925 that Republicans controlled the House, Senate, governorship and Supreme Court (while the justices are nonpartisan, they are nominated by state parties.)

Ballenger is a former Republican lawmaker. But under the one-party control in 2001, he alleged, “they rammed through a real gerrymander, and in 2011 it happened all over again.”

Republican Gov. Rick Snyder is standing by the maps he signed into law in 2011.

“Gov. Snyder believes the districts are just as constitutional as he did when he signed the law six years ago,” said Snyder spokeswoman Anna Heaton.

Brewer plans to name the State of Michigan as the lawsuit’s defendant and individual voters as plaintiffs, although he does not yet have an estimated filing date. If the plaintiffs prevail, Brewer said, Michigan Republicans would have to redraw the maps taking the new standard into account.

Nationally, there have been efforts to change the way redistricting happens overall. Former U.S. Attorney General Eric Holder is leading an effort to help Democrats hit back on maps that, as Holder put it to the New York Times, have politicians picking their constituents instead of the other way around. And advising that commission is Democrat and former Michigan U.S. Rep. Mark Schauer.