In a decision issued on Monday, Administrative Law Judge Benjamin Green said Amazon supervisors told workers that they would miss out on regularly scheduled raises and improved benefits if the company was forced into lengthy union negotiations.

US labour law prohibits employers from making threats or promises in order to discourage unionising.

Workers at Amazon’s JFK8 fulfillment centre in Staten Island voted to join the Amazon Labor Union (ALU) last April, a first for the company in the United States. In May, employees at a smaller nearby storage facility rejected a union campaign.

Green said Amazon also violated federal labour law in 2021 by removing a post from an internal message board asking workers to sign a union-backed petition to make Juneteenth a paid holiday.

Amazon did not immediately respond to a request for comment. Nor did the ALU.

The board’s general counsel, which acts as a prosecutor, is trying to use the case to convince the five-member board to ban mandatory anti-union meetings. So-called captive audience meetings have for decades been a common tool used by employers to discourage unionising.

Green did not rule on that issue because administrative judges cannot make new legal precedent. But the board will likely take up the issue if Amazon appeals.

Amazon has faced dozens of complaints from workers and the ALU as the union attempts to organize warehouses across the country. The company has generally denied wrongdoing.

Earlier this month, an NLRB official rejected Amazon’s bid to overturn the results of the JFK8 election. The company said it intends to appeal that ruling to the board.

(Reporting by Daniel Wiessner in Albany, New York; Editing by Mark Potter.)