The Workers United union has alleged that Tesla fired over thirty employees from its Buffalo, New York plant just one day after workers there made public their plans to form a union, the organization said in a press release. At least one of the workers was part of the 25-employee organizing committee, while several others had taken part in labor discussions, according to a complaint filed with the US National Labor Relations Board (NLRB).

The complaint, which was reported first reported by Bloomberg, alleges that the firings came “in retaliation for union activity and to discourage union activity.” The Workers United union is seeking a federal court injunction to protect employee rights in its NLRB filing. “This is a form of collective retaliation against the group of workers that started this organizing effort” and is “designed to terrify everyone about potential consequences of them organizing” said Workers United organizer Jaz Brisack, who helped with the union drive.

Retaliation against organizing unions is illegal under US federal law, and complaints with the NLRB can lead to fired workers being reinstated with backpay, Bloomberg notes.

The Buffalo facility, which is also known as Gigafactory 2, is home to over 800 analysts tasked with labeling vision data to train Tesla’s Autopilot software. Bloomberg reports that employees have complained of excessive monitoring (including tracking keystrokes) and productivity targets that are so high that employees have felt pressured to not visit the bathroom. Workers are also seeking better job security and pay. The union also hopes to organize the 1,000 manufacturing employees based in Buffalo.

Bloomberg’s report doesn’t say how Tesla justified the firings. However, it reports that the company warned employees about technology usage in the workplace, and called on them to “protect the confidentiality, integrity and security of all Tesla Business Information.” The warning came a day after a Bloomberg report was published containing quotes from various employees at the factory. Nearly 200 employees that were doing similar Autopilot training work were fired from Tesla’s California operations last year.

Tesla and its CEO Elon Musk have faced numerous complaints over their alleged anti-union behavior over the years. In September 2019, a California judge found the company guilty of several illegal anti-union practices including letting security guards harass employees who were handing out union leaflets, and interrogating union organizers. The judge also ruled that an anti-union tweet from Musk was illegal, and in 2021 the NLRB eventually ordered Tesla to tell Musk to delete the tweet. As of this writing the tweet remains up, however, and Tesla workers are yet to form a union.

Tesla did not respond to a request for comment sent to the press email address listed on its website, but is widely reported to have disbanded its press team three years ago. Shortly after sending a request for comment, The Verge received a bounceback from the email address, indicating that its inbox is now full and can’t accept new messages.

Update February 16th, 7:44AM ET: Updated with The Verge’s confirmation of the NLRB complaint.