No Labels, the group preparing for a possible third-party presidential campaign, can prohibit members from using its ballot line to run for office in Arizona, a federal judge ruled Tuesday.

The decision protects the group's efforts to maintain control and secrecy around its operations and finances as Donald Trump critics warn that No Labels could help return Trump to the White House by siphoning voters who might otherwise vote for President Joe Biden.

A judge blocked Arizona Secretary of State Adrian Fontes from recognizing candidates wanting to run for office under the No Labels banner aside from the party's yet-to-be-chosen ticket for president and vice president.

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Fontes, a Democrat, called the ruling "dead wrong" and vowed to appeal. He warned that the ruling could keep the nearly 19,000 No Labels party members from voting in a primary, and the precedent could allow party bosses to decide who can run for office from any party.

"This current decision will disenfranchise almost 19,000 registered Arizona voters, and if it stands, it could potentially derail the entire candidate nomination process," Fontes said in a statement.

No Labels officials said the ruling "strongly vindicates our constitutional rights."

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A worker walks back stage after presidential candidate Florida Gov. Ron DeSantis spoke during a caucus night party on Jan. 15, 2024, in West Des Moines, Iowa. As No Labels prepares for a possible third-party presidential campaign, speculation abounds regarding who would appear on their ticket. (AP Photo/Charlie Neibergall)

"Our ballot line cannot be hijacked. Our movement will not be stopped," Dr. Benjamin F. Chavis, Jr., a No Labels national co-chair, and former Missouri Gov. Jay Nixon, the group's director of ballot integrity, said in a statement.

No Labels has drawn increasing scrutiny as it spends tens of millions of dollars to secure ballot access in all 50 states by Election Day. The group's critics have pushed for transparency around its donors, whom No Labels leaders have refused to name, and had hoped that state campaign finance laws could help pry information loose.

But the Arizona ruling could support the No Labels argument that it doesn’t have to file campaign finance disclosures under Arizona law because it is not supporting any candidates for state office.

Arizona, likely to be among the closest battlegrounds in November, is among 13 states where No Labels has already secured its place on the ballot. Biden won the state by fewer than 11,000 votes in 2020 with a coalition that included conservative independents and moderate Republicans, prompting worry among Democrats that a No Labels candidate could tip the state to Trump even with a tiny showing in a state with more than 3 million voters.

Judge John Tuchi, a Barack Obama appointee, ruled that No Labels has a First Amendment right to determine whom it wants to associate with.

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Fontes had argued that he's obligated to accept filings from candidates even if party leaders reject them. Tuchi agreed, but said that requirement was trumped by the need to protect No Labels' constitutional rights.

Richard Grayson, one of five No Labels members who have filed to run for office in Arizona, said he was hopeful appellate courts would see the issue differently. Trump, the clear leader of the Republican Party, can't tell candidates he doesn't like that they can't run for state Legislature, he said.

"There’s a lot of people in the various parties that the parties don’t want them to run, and that’s always been true," Grayson said Tuesday.

Grayson, who likens his perennial losing campaigns to performance art, is a No Labels critic who thinks the party should disclose its donors. He changed his party affiliation to draw attention to what he views as a top-down operation that's doomed to failure.