The National Labor Relations Board (NLRB) has found that Tesla violated US labor laws by firing a union activist and threatening workers’ benefits via a tweet from CEO Elon Musk. As a result, the company must reinstate the fired worker and force Musk to delete the tweet in question, Bloomberg has reported.

Musk’s tweet, from May of 2018, immediately drew attention as a possible violation of labor laws. In it, he said that “nothing stopping Tesla team at our car plant from voting union. Could do so tmrw if they wanted. But why pay union dues and give up stock options for nothing?” Tesla argued that the tweet pointed out that union members from other automakers don’t receive stock options. However, former NLRB chair Wilma Liebman argued that Tesla workers may see it differently. “The employee is going to hear it as, ‘If I vote to unionize, stock options will no longer be an option,'” she told Bloomberg at the time.

In its ruling, the NLRB said that the fired employee, Richard Ortiz, must be rehired with all mentions of disciplinary action removed from his personal files. The company must also “make him whole for any loss of earnings and other benefits.”

In addition, it ordered Tesla to make Musk delete the tweet in question and post a lengthy notice to employees about the ruling, stating their rights to “form, join, or assist a union.” The notice must also say that workers won’t be terminated or disciplined for such activities and that the company will rehire Ortiz with back pay. While an administrative judge recommended that Musk should read the notice aloud to workers in a meeting, the NLRB said that the written notice would suffice.

Tesla has yet to comment, but NLRB rulings can be appealed in a federal court. However, the board can’t impose punitive damages nor hold executives liable for breaking the law, Bloomberg noted. As of today (March 26th at 7:01 AM ET), Musk’s tweet is still live.

The ruling also caught the attention of union officials and advocates, who said it came far too late. “Here is a company that clearly broke the law and yet it is three years down the road before these workers achieved a modicum of justice,” United Autoworkers VP Cindy Estrada told Bloomberg.