The online retailer says his termination was completely unrelated to the union effort.

An Amazon employee who was leading efforts to unionize workers in Staten Island is taking legal action against the company for firing him last month.

Rashad Long, who worked the overnight shift at Amazon’s new warehouse in New York City, was fired last month by one of his managers for a safety violation, according to a complaint Long filed Wednesday with the National Labor Relations Board, a federal agency that enforces fair labor laws.

In his complaint, which was first reported by the New York Times, Long said that terminating him for a safety violation was just a cover for the real reason: Supervisors were punishing him for speaking out about working conditions at the warehouse.

Amazon warehouse employees announced in December they were trying to organize with the Retail, Wholesale, and Department Store Union. Long was the most outspoken about his frustration at work. During a press conference in December and in media interviews, Long accused managers of forcing employees to work 12-hour shifts five or six days in a row. He said the company treated workers like robots, and he felt unsafe in the warehouse.

Two months later, on February 8, Long broke a minor safety rule when he picked up an item that had fallen off a robot and put it back on the machine, an attorney for the labor union wrote in the complaint, which was shared with Vox.

Long was fired “for engaging in protected, concerted activity by speaking out about the abhorrent working conditions at the Amazon fulfillment facility located on Staten Island,” the complaint said.

Amazon denies the accusation.

“Mr. Long’s allegations are false,” Rachael Lighty, a spokesperson for Amazon, said in a statement to Vox. “His employment was terminated for violating a serious safety policy. All employees, including Mr. Long, are trained from day one on the importance of safety and their role in maintaining a safe workplace.”