Lansing — A Democratic group filed a lawsuit in federal court Wednesday challenging Michigan's laws that allow absentee votes to be thrown out if voters' signatures don't match other documents filed with election officials.

The super political action committee, Priorities USA, described as a "progressive advocacy and service" nonprofit organization, alleged that Michigan's process for determining whether absentee voters' signatures are valid violate residents' due process and equal protection rights.

"The burden that these laws impose on the right to vote is undeniable and unjustified," Priorities USA's lawsuit says. "Any potential concerns about voter fraud in the absentee voting process are already effectively addressed by other Michigan laws ..."

The Michigan Republican Party criticized the lawsuit as an attempt to undermine election security and unfairly help Democratic candidates.

"This lawsuit is yet another example of liberals trying to strip away election security measures for their own benefit," Michigan Republican Party Chairwoman Laura Cox said in a Wednesday statement.

"If it were to be successful, it could open the door to massive voter fraud in our state and call the legitimacy of Michigan’s absentee ballots into question. The Michigan Republican party stands committed to ensuring the integrity of our state’s election process.”

More lawsuits potentially affecting state elections law are expected by the Democratic group.

"This is just the first shoe to drop in MI," Priorities USA Chairman Guy Cecil tweeted Wednesday. "More to come."

According to the lawsuit, local clerks in Michigan must compare a voter's signature on an absentee ballot application with the signature in the state's qualified voter list. If the signatures don't match, the clerks must reject the application.

Then, when a voter submits an absentee ballot, clerks must determine whether the signature on the ballot matches a reference signature for the voter. If they don't match, clerks must reject the ballot, according to the lawsuit, which alleges there is no uniform process for determining whether signatures match.

"In fact, no one really knows how Michigan election officials decide whether a signature on an absentee ballot or ballot application is sufficiently similar to the previously designated signature to withstand scrutiny," according to the suit by the Democratic super PAC.

Priorities USA is one of at least two Democratic super PACs that has been spending big money in Michigan, targeting working-class voters who help elected President Donald Trump in 2016. The Priorities super PAC said it planned to spend $100 million through early 2020 across Michigan, Florida, Wisconsin and Pennsylvania in its first phase of spending.

An early six-figure digital buy has financed ads across the states that accuse Trump of breaking his promise to put regular Americans’ needs ahead of interest groups.

Michigan's "arbitrary and standardless signature matching laws" have disenfranchised hundreds of voters in recent elections based on subjective decisions made by election officials, the lawsuit alleges. The suit cites a survey that found Michigan had rejected more than 1,200 absentee ballots since the 2012 general election.

According to Priorities USA, the signature matching laws unfairly burden the right to vote in Michigan and go against the Equal Protection Clause of the 14th Amendment of the U.S. Constitution because the laws have been implemented differently across the state.

The lawsuit was filed in the Eastern District of Michigan, where Democratic-nominated judges hold a 14-6 advantage and are more likely to be selected in the random draw process. Republican-nominated judges have a 4-0 edge in the Western District of Michigan, which covers Lansing, the home of state government.

The lawsuit comes a year after Michigan voters approved a ballot proposal in November 2018 that allows for no-reason absentee voting.

It also comes after Priorities USA Foundation contracted a third party to send hundreds of public records requests to clerks throughout Michigan asking for copies of ballots and accompanying materials from the November 2016 election.

The attorneys working on the case for Priorities USA include Marc Elias, who was general counsel for Hillary Clinton's 2016 campaign for president.

The lawsuit specifically names Jocelyn Benson, Michigan's Democratic secretary of state who is in charge of enforcing state election laws and took office at the start of January. Benson's office said it hadn't received the lawsuit as of 1 p.m. Wednesday.

cmauger@detroitnews.com