The Communication Workers of America (CWA) said it filed a complaint with the U.S. National Labor Relations Board Tuesday seeking to have the workers reinstated.

The case is the latest the union has brought to the labor board as part of a campaign to unionize the firm and its subsidiaries. Small groups of game testers at three Activision subsidiaries voted to join the CWA last year.

Microsoft Corp. is seeking to acquire Activision for $69 billion, but U.S. regulators have sued to block the deal.

The labor board last year issued complaints accusing Santa Monica, California-based Activision of threatening employees who posted on social media about their working conditions and withholding raises from pro-union workers, which the company denies.

Joseph Christinat, a spokesman for Activision, said the company takes appropriate disciplinary action when employees violate its workplace code of conduct.

“Using abusive, threatening or harassing language toward colleagues is unacceptable and we are disappointed that the CWA is advocating for this type of behavior,” he said.

According to the union, Activision last month announced its employees would be required to report to the office three days per week beginning in April, ending a policy that had allowed more flexible arrangements during the COVID-19 pandemic.

The change received an overwhelmingly negative response from employees, the CWA said, and Activision fired two game testers who "expressed their outrage using strong language."

The CWA suggested the Democrat-led labor board could use the case to revisit a 2020 ruling by a Republican majority that limited legal protections for workers who use vulgar or offensive language during workplace disputes.

"When faced with unfair treatment by unscrupulous employers like Activision, workers should have the right to express themselves," CWA Secretary-Treasurer Sara Steffens said in a statement.