WASHINGTON — When Larry Harmon of Akron, a Navy veteran and software engineer, went to his local polling place to vote in 2015, he discovered he was no longer on the list of registered voters.

On Wednesday, the U.S. Supreme Court is taking up his challenge to the system Ohio used to remove him and others from the database. Civil rights groups say it discourages minority turnout, but the state says it's an important tool in the task of keeping voter registration lists accurate and up to date.

"If the court sides with Ohio," said Professor Rick Hasen, an election law expert at the University of California at Irvine, "you'll see more red states making it easier to drop people from the voter registration rolls, and it's going to continue what I call the voting wars between the parties."

For the Supreme Court, the issue is what a state can assume from a resident's failure to cast a vote in more than one election. Harmon's decision to sit out two successive elections started the state's effort to cancel his registration.

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As many states do, Ohio compares change-of-address data from the U.S. Postal Service with its state registration list to identify voters who have moved without updating their addresses. A local election boards mails notices to those who appear to be ineligible to vote. If they do not respond or vote during the following four years, their registration is canceled.

Voting rights activists rally outside the Supreme Court Wednesday. Michael Reynolds / EPA

At issue in the Supreme Court is an alternative method Ohio uses to identify people who have moved. The state sends notices to those who fail to cast a ballot during a two-year period. Those who do not respond and don't vote over the next four years (including in two more federal elections) are dropped from the list of registered voters.

It was that supplemental system that dropped Harmon from the rolls. The state says he was sent a notice. He says he doesn't remember getting it.

Larry Harmon stands outside of his home in Kent, Ohio. Harmon was removed from the voting rolls after not voting in the last election. Maddie McGarvey / for NBC News

A federal appeals court ruled that Ohio's supplemental system violated a federal law, the National Voter Registration Act, which says voters can be purged from the rolls only if they ask, move, are convicted of a felony, become mentally incapacitated or die. A failure to vote, the court said, should not trigger the beginning of the purging process.

The A. Philip Randolph Institute, a civil rights group, led the effort to challenge Ohio's system, arguing that poor and minority residents are the hardest hit.

But Ohio says the failure to respond to a notice, not a failure to vote, leads the state to remove a voter from the roles. Trump's Justice Department, reversing the position taken under the Obama administration, is defending Ohio's method.

"Registrants removed using that procedure are not removed by reason of their initial failure to vote. They are sent a notice because of that failure, but they are not removed unless they fail to respond and fail to vote for the additional period prescribed," the Justice Department said in a court filing.

The outcome will directly affect Ohio and six other states that have similar laws — Georgia, Montana, Oklahoma, Oregon, Pennsylvania and West Virginia. More than a dozen other states have indicated they would like to adopt the same system.

The court will decide the case by late June.