A U.S. appeals court on Monday ruled that it lacks authority to hear Amazon.com’s constitutional challenge to the structure of the National Labor Relations Board, widening a growing split among federal circuits over similar lawsuits.

A unanimous three-judge panel of the San Francisco-based U.S. Court of Appeals for the Ninth Circuit said Amazon’s lawsuit could not proceed because it arose from an underlying labor dispute, placing it outside the jurisdiction of federal courts under longstanding labor law.

Amazon’s case stems from an NLRB administrative proceeding accusing the company of being a joint employer of delivery drivers hired by contractor Battle Tested Strategies and of unlawfully failing to recognize and bargain with their union. Amazon denies wrongdoing in that matter.

The Ninth Circuit said federal law bars courts from intervening in disputes that involve or grow out of labor conflicts, citing the Norris-LaGuardia Act, which limits courts’ power to issue injunctions in labor-related cases.

“Amazon’s requested injunction would impede union activities, the very outcome the Act was enacted to prevent,” Circuit Judge Danielle Forrest wrote for the panel.

The ruling comes amid a wave of more than 40 lawsuits filed nationwide since late 2023 challenging various aspects of the NLRB’s structure and enforcement authority. Many of those suits seek to halt ongoing board proceedings by arguing that removal protections for NLRB members and administrative law judges are unconstitutional.

Amazon argued that NLRB proceedings violate the Constitution because federal law prevents the board’s five members and its judges from being removed without cause. Earlier this month, the U.S. Court of Appeals for the District of Columbia Circuit agreed in part, ruling that NLRB members cannot be shielded from at-will removal and upholding President Donald Trump’s dismissal of Democratic board member Gwynne Wilcox.

A federal district judge in California rejected Amazon’s request for a preliminary injunction in February, finding that the Norris-LaGuardia Act barred judicial intervention. The Ninth Circuit affirmed that decision Monday.

The panel said Congress enacted the law to prevent courts from interfering with workers’ labor rights while NLRB cases are pending, even when employers raise constitutional objections.

The judges on the panel were Forrest, Jacqueline Nguyen, and Lawrence VanDyke. Forrest and VanDyke were appointed by Trump, while Nguyen was appointed by former President Barack Obama.

Amazon and the NLRB did not immediately respond to requests for comment.

The decision deepens a split among appellate courts. Earlier this month, the Third Circuit in Philadelphia reached a similar conclusion in a case brought by a New Jersey nursing home. By contrast, the Fifth Circuit, based in New Orleans, ruled in August that removal protections for NLRB members and judges are invalid and that the Norris-LaGuardia Act does not bar employer lawsuits against the agency.

The Fifth Circuit held in cases involving SpaceX and other companies that disputes between employers and the NLRB itself do not qualify as labor disputes under the statute.

The Ninth Circuit rejected that interpretation, saying the law’s plain language bars courts from intervening in cases connected to employment disputes, even if the court challenge is not itself a labor dispute.

“It need not itself be a labor dispute,” Forrest wrote.

The court noted that its ruling does not prevent employers in the Ninth Circuit from challenging the NLRB’s structure altogether. Companies may raise those arguments during administrative proceedings and seek judicial review if they lose before the board.

The case is Amazon.com Services LLC v. National Labor Relations Board, No. 25-886, in the U.S. Court of Appeals for the Ninth Circuit.