(CNN) A legal complaint filed by a conservative law firm in Wisconsin is arguing that the state should remove 234,000 voters from the state's voter rolls because they may have moved recently.
The complaint, filed Tuesday by the Wisconsin Institute for Law and Liberty against members of the Wisconsin Elections Commission, says state law requires the commission to remove from the active voting rolls voters who don't respond to a recent mailing, made as part of a regular effort to update voter rolls, within 30 days.
The commission, however, says it's allowing voters to stay on the rolls through the spring of 2021, based on a June vote by the commission.
"State agencies comprised of political appointees and unelected staff do not have the authority to invent or amend policy contrary to state law," the institute's president and general counsel, Rick Esenberg, said in a statement.
"Whatever the intent of the Wisconsin Election(s) Commission's action, it is illegal and must be remedied immediately."
The institute is "committed to classical liberalism and constitutional government," according to its website.
It has a history of focusing on conservative causes, recently working on cases related to school choice and defending the Second Amendment.
In a statement Wednesday afternoon, Meagan Wolfe, the state's chief election official, said "the commission is confident that it is complying with Wisconsin law."
Last week, the commission sent out letters to about 234,000 registered voters who have told another government agency, such as a post office or Department of Motor Vehicles, they have recently moved.
In her statement, Wolfe said the commission sent out the mailing based on "lessons learned" from its 2017 mailing to update the voter rolls, with an eye toward making the process more "user-friendly."
One of those changes is that voters who get the mailing this year won't be automatically taken off the state's active voter list if they don't respond within a month.
They'll stay on the list through the April 2021 election. If they don't vote by then, they'll be deactivated, the commissions said.
Voters in Wisconsin must register online or by mail 20 days before Election Day, according to Vote.org. If they miss that deadline, voters may still register in person up through Election Day.
As of June 2019, the state had 3.4 million registered voters, making up about 76% of the state's voting-age eligible population.
Analiese Eicher, who heads the One Wisconsin Institute, told CNN the recent complaint against the Wisconsin Elections Commission could negatively affect demographics groups that tend to vote Democrat.
And she said the complaint follows a national trend.
"We've seen voter roll purges across the country that affect young people, people of color and those who move often," she said. "It's unfortunate that it's come to Wisconsin."
Eicher said conservatives are working to make whatever gains they can to win elections in the state.
In 2016, Wisconsin helped add 10 electoral votes to Donald Trump's column in the Electoral College. He won the state by less than 1%, garnering just under 23,000 more votes than Hillary Clinton.
CORRECTION: This story has been updated to correct how long voters have to register in person in Wisconsin.