Musk issued the tweet as the United Auto Workers was seeking to organize employees at Tesla’s plant in Fremont, California.

“Nothing stopping Tesla team at our car plant from voting union. Could do so tmrw if they wanted,” he wrote. “But why pay union dues & give up stock options for nothing?”

The appeals court panel found “substantial evidence” that the tweet was “an implied threat to end stock options as retaliation for unionization.”

In seeking reconsideration, Tesla cited free speech concerns, and said the NLRB ignored that no employees claimed that Musk was threatening them, that Musk did not intend to threaten anyone, and that Musk later clarified his tweet was not a threat.

The NLRB did not immediately respond to requests for comment. Tesla and its lawyers did not immediately respond to similar requests.

A decision is unlikely before 2024.

Musk’s use of Twitter has caused him trouble before, including when he tweeted in August 2018 about having “funding secured” to take Tesla private.

Musk did not, and he and Tesla each paid $20 million civil fines to settle a subsequent U.S. Securities and Exchange Commission lawsuit.

Musk bought Twitter last October for $44 billion.