A federal appeals court ruled Friday that the billionaire must delete his 2018 Twitter post suggesting that Tesla Inc. workers could lose stock options if they formed a union, as it violated labor law. Must tweeted:

"Nothing stopping Tesla team at our car plant from voting union. Could do so tmrw if they wanted. But why pay union dues & give up stock options for nothing? Our safety record is 2X better than when plant was UAW & everybody already gets healthcare."

The decision is a victory for the National Labor Relations Board and a blow to Tesla, which has vehemently opposed the United Auto Workers’ years-long effort to unionize the electric-vehicle maker’s workers.