The New York State Board of Elections is violating the Constitution and federal election law when it designates certain registered voters as “inactive” and keeps those names out of its poll books during elections, according to a decision issued in federal court late Friday .

District Judge Alison J. Nathan wrote that New York State’s refusal to provide “inactive voter lists” at polling sites during an election violates the Equal Protection Clause of the 14th Amendment and ordered the state to make those lists available going forward. She also found the state was violating the National Voter Registration Act of 1993 when it moved voters to the inactive list.

Up to now, voters would be designated as “inactive” if the post office marked mail from the Board as undeliverable, or if there was a question about whether a voter still resided at a specific address.

Of the state’s nearly 13 million registered voters, more than one million are designated as inactive—nearly half a million residing here in New York City.

Listen to Brigid Bergin's report on WNYC:

In October, the Court held a four-day bench trial. Then late last Friday, Judge Nathan issued a 60-page opinion ordering the state to ensure the names of all inactive voters are available at poll sites—along with all other registered voters.

Judge Nathan wrote that the state improperly designated tens of thousands of votes as “inactive” even though the individuals continue to live at the address where they are currently registered to vote. She blamed problems with the U.S. Postal Service and the national change of address registry for providing unreliable information—something that local election officials corroborated in their own testimony during the trial.

“The quality of the information that we get from the United States Post Office is the linchpin to the success of the inactivity process,” Michael Ryan, executive director of the New York City Board of Elections, testified during the trial. He also said the city has uncovered, “significant issues with the consistency of the information we get from the post office.” Robert Brehm, the Co-Executive Director of the State Board of Elections also testified to problems with relying on post office information.

The decision marks the latest victory for Common Cause, the plaintiff in the case, and the Lawyers Committee for Civil Rights Under Law, LatinoJustice PRLDEF, and the law firm Dechert LLP, which filed the lawsuit in 2017 on the good government group’s behalf.

“We're really glad that the federal court has stepped in to instruct the state that they can not arbitrarily remove people from the voting rolls based on one piece of mail being returned,” said Susan Lerner, head of Common Cause New York.

John Powers, one of the attorneys from the Lawyers Committee, said this ruling is particularly important to voters here in New York City, who disproportionately end up on the inactive voter list.

“Tens of thousands of New York voters who appear at the polling place are going to be able to find their names on a list that they wouldn't have been able to find had this decision not been issued,” Powers told WNYC / Gothamist noting that this decision came down early enough that he anticipates the state can make the necessary procedural changes ahead of what is expected to be a high-turnout presidential primary in April.

The State Board of Elections has not yet responded to a request for comment.

This latest case is an outgrowth of the work these groups did in the aftermath of a massive voter purge in Brooklyn ahead of 2016 presidential primary, which led to another decision against the New York City Board of Elections over how it maintained its voter rolls.

As the attorneys investigated the voter purge case, they found thousands of registered voters whose names did not appear in any poll books during elections. Those people were voters the state designated as “inactive” because the post office returned a piece of mail intended for the voter as undeliverable. While those voters weren’t technically purged, some were still disenfranchised because either they were never offered an affidavit ballot at their poll site or they were sent to vote at the wrong location.

That’s exactly what happened to Lauren Wolfe when she tried to vote in the 2016 general election. When poll workers could not find her name on the rolls, she was directed to go to another location. She went back and forth between poll sites and ultimately cast an affidavit ballot at what she would only find out months later was the wrong poll site. Her vote did not count. But she’s hopeful this ruling will prevent something like that in the future.

“The idea is that this decision will make sure, or should make sure, that all eligible voters' names are contained in poll books for future elections,” Wolfe said to WNYC / Gothamist on Sunday. At a minimum, that means someone who has to cast an affidavit ballot in the future can be more assured that their vote will count because they will know they are in the right location, “and that is extremely gratifying,” Wolfe added.

Brigid Bergin is the City Hall and politics reporter for WNYC. You can follow her on Twitter at @brigidbergin.