The US labor board is abandoning a years-long legal battle against Elon Musk’s SpaceX and signaling it will steer clear of future cases against the company, according to a letter from the board cited by the New York Times and Bloomberg.

Two years after issuing a complaint accusing the aerospace firm of firing eight engineers because of their involvement in an open letter criticizing Musk, the National Labor Relations Board (NLRB) said it was dismissing the case, disclaiming jurisdiction over it, according to the letter.

In a letter to the attorneys of the former employees, the labor board cited a recent opinion issued by a separate agency, the National Mediation Board, arguing that SpaceX engineers belonged under its jurisdiction rather than NLRB’s.

Danielle Pierce, a regional director of the agency said: “Accordingly, the National Labor Relations Board lacks jurisdiction over the Employer and, therefore, I am dismissing your charge.”

SpaceX and the National Mediation Board did not immediately respond to requests for comment. The NLRB declined comment on the report.

In August last year, a US appeals court agreed with SpaceX and two other companies that the NLRB’s structure was probably unlawful and blocked the agency from pursuing cases against them.

The National Mediation Board oversees railroad and airline companies such as American Airlines Group, while the NLRB oversees most other private sector employers, including manufacturers like Boeing.

Under federal law, workers covered by the NLRB have a right to participate in a wide range of collective action aimed at improving their working conditions, with or without a union. Workers under National Mediation Board jurisdiction are covered by a different law, which lacks equivalent protections, the report said.