A federal judge has blocked New Jersey’s unusual county line system — used by New Jersey’s powerful political machines to help sway elections — from being used in the June primary race.

The decision by U.S. District Judge Zahid Quraishi came in a suit brought by U.S. Senate race frontrunner Andy Kim.

Quraishi awarded Kim and two other plaintiffs — South Jersey congressional candidates Sarah Schoengood and Carolyn Rush — a preliminary injunction that will force clerks in the 19 New Jersey counties, out of 21 total, that use the “line” system to redesign ballots before the election.

“The Court wishes to make clear that it recognizes the magnitude of its decision,” Quraishi wrote. “The integrity of the democratic process for a primary election is at stake and the remedy Plaintiffs are seeking is extraordinary.”

Under the county line system, candidates running on a ticket or slate are bracketed together in a single line or row. That means candidates endorsed by county political organizations, for any office, all appear on a line together. This year, that line will be headed by President Joe Biden. Researchers say voters are inclined to tick off all the boxes in that line, which appears more legitimate because of the associations with candidates in major races. One study found a double-digit advantage for Congressional candidates running on the line across 45 races.

Under Quraishi’s order, counties will instead have to use an “office block” ballot format, where all candidates for a given office are grouped together.

“Today’s decision is a victory for a fairer, more democratic politics in New Jersey,” Kim said in a statement sent by his campaign. “It’s a victory built from the incredible grassroots work of activists across our state who saw an undemocratic system marginalizing the voices of voters, and worked tirelessly to fix it.”

Kim has positioned himself as a good-government reformer in his bid for the seat currently held by Sen. Bob Menendez, who is facing a federal indictment alleging he took bribes in exchange for helping foreign governments and tried to interfere in criminal cases.

Kim’s primary competitor in the Senate race, until recently, had been First Lady Tammy Murphy. Kim had argued in the case that Murphy had a huge institutional advantage in the race, since many county political organizations were set to award her the county line — in some cases, only on the say-so of the party chairs who run those organizations.

But Murphy dropped out of the race Sunday. Kim accepted endorsements from county organizations previously expected to support Murphy, which meant he was set to appear on the line throughout most of New Jersey himself.

In filings this week, clerks opposing the change to the ballot system argued Murphy’s departure fundamentally changed the race, but Kim’s lawyers countered that the ballot remained undemocratic in its current design — even if he could personally benefit from it now — and that it continued to harm the other plaintiffs in their own races.

Clerks had argued they’d have limited time to change ballots before the election, and that doing so could confuse voters.

This is a developing story and will be updated.