In 2015, Larry Harmon, a 59-year-old software engineer and Navy vet, went to the polls in his hometown of Kent, Ohio, to vote on a state ballot initiative. But poll workers told him he was no longer registered and could not vote.

“I felt embarrassed and stupid at the time,” Harmon told Reuters. “The more I think about it, the madder I am,” he said.

Harmon voted for Barack Obama in 2008, but had not returned to vote until 2015. He later learned that he was purged from the rolls in Ohio for “infrequent voting” because he had not voted in a six-year period, even though he hadn’t moved or done anything to change his registration status. From 2011 to 2016, Ohio purged 2 million voters from the rolls—1.2 million for infrequent voting—more than any other state.

Harmon challenged Ohio’s voter purge in court, with the assistance of groups like Demos and the ACLU of Ohio, and in September 2016, the US Court of Appeals for the Sixth Circuit ruled in his favor, finding that Ohio’s removal of “infrequent” voters violated the 1993 National Voter Registration Act, which says voter-roll maintenance “shall not result in the removal of the name of any person from the official list of voters registered to vote in an election for Federal office by reason of the person’s failure to vote.” As a result, 7,500 people who would have otherwise been purged were able to vote in the 2016 election, including Harmon, according to Secretary of State Jon Husted.

Ohio appealed to the Supreme Court and today, to the dismay of voting-rights activists, the Supreme Court decided to hear the case next term. If the Court reverses the Sixth Circuit and rules in favor of Ohio, it could make it easier for states to purge the voting rolls in inaccurate and discriminatory ways. (Fifteen Republican-controlled states, including Kris Kobach’s Kansas, filed an amicus brief supporting Ohio’s position.) This will be the first major voting-rights case heard since Neil Gorsuch took the bench, reviving the Court’s 5-4 conservative majority.

“We’re very disappointed because we believe the Sixth Circuit ruled correctly,” says Freda Levenson, legal director of the ACLU of Ohio. “It was a very important ruling.… There were hundreds of thousands of voters who were illegally purged.”

At least 144,000 voters in Ohio’s three largest counties, home to Cleveland, Columbus, and Cincinnati, were purged since the 2012 election, with voters in Democratic-leaning neighborhoods twice as likely to be removed as those in Republican-leaning ones, according to a Reuters analysis. These cities are heavily Democratic, with large minority populations, and there was a clear partisan and racial disparity to the state’s voter purge.

In Cleveland’s Cuyahoga County, 5 percent of voters in neighborhoods that backed Obama by more than 60 percent in 2012 were purged last year due to inactivity, according to the Reuters analysis of the voter lists. In neighborhoods where Obama got less than 40 percent of the vote, 2.5 percent of registered voters were removed for that reason.

In Franklin County, home to the state capital Columbus, 11 percent of voters in Democratic-leaning neighborhoods have been purged since 2012 due to inactivity. Only 6 percent of voters in Republican-leaning neighborhoods have been purged.

The disparity is especially stark in Hamilton County, where affluent Republican suburbs ring Cincinnati, which has one of the highest child-poverty rates in the country.

In the heavily African-American neighborhoods near downtown, more than 10 percent of registered voters have been removed due to inactivity since 2012. In suburban Indian Hill, only 4 percent have been purged due to inactivity.

The purge worked like this: If a voter missed an election, Ohio sent them a letter making sure their address was still current. If the voter didn’t respond, Ohio put them on an inactive list, and if the voter didn’t vote in the next two elections, they were removed from the rolls.

In addition to the partisan and racial disparities, the state’s non-voter list was riddled with errors, reported the Akron Beacon Journal:

In Summit County, 36,822 registered voters will not get an absentee ballot application mailed to them. This includes 10,901 who voted in the 2008 presidential election (80 percent of whom voted Democratic in the contested primaries that year) and 123 who voted as recently as this March.

Kristina Hall, a lab courier who’s lived in Cuyahoga Falls for the past four years, can’t figure out why she’s one of them.

Hall voted in the Democratic Party primary in March. When she arrived at her polling location, she was told she was not on the list. An elections worker gave her a provisional ballot. Her vote, after everything checked out, was supposed to be used to update her address, which apparently was out of date with county election records.

It didn’t. An active voter in every presidential election in Ohio until she moved briefly to New York in 2012, Hall swears she voted in 2014 when she returned. State records show she didn’t.

The hassle has driven her to skepticism, especially since she said she’s received three notices from the board of elections to update her address and get off “confirmation status.” She said she sent all three back and has voted twice since they first arrived last year.

“I get so mad when people don’t vote,” she said. “That’s why I thought it was a problem when I’ve done everything I’m supposed to.”

This isn’t the first time a controversial voter purge in Ohio has attracted scrutiny. In 2004, the Ohio Republican Party sent a mailing to 232,000 newly registered voters, urging them to vote Republican. When 35,000 mailers were returned as undeliverable, the GOP tried to purge those voters from the rolls. As I reported in my book Give Us the Ballot, “more than half the challenged voters lived in Ohio’s two most populous counties—Cuyahoga (Cleveland) and Franklin (Columbus)—which were overwhelmingly Democratic and heavily minority.” The DNC sued the RNC and a federal court blocked the purge, ruling that voters “faced irreparable injury” to their “constitutional right to vote.”

But Republican-led voter purging efforts proved disastrous during the 2000 election in Florida, when the state wrongly labeled 12,000 registered voters as ex-felons and scrubbed them from the voter rolls—a number that was 22 times George W. Bush’s 537-vote margin of victory. That election taught the unfortunate lesson that a small manipulation of the country’s voting laws could make a big difference in close elections.

There were problems in Ohio in 2016 even after the Sixth Circuit ruled against the state’s purge. One in seven registered voters were not mailed absentee ballot applications because they were labeled inactive or were thought to have moved.

Freda Levenson told me a story of a 104-year-old-blind woman who couldn’t vote in 2016 because she was removed from the rolls at 102. She last voted in 2008 and was purged in 2015. As a result, her request for an absentee ballot in 2016 was denied.

“Here’s the problem: people don’t realize when they’re purged,” says Levenson. “In Ohio, voting is use it or lose it.”