DETROIT (AP) — Elon Musk is inviting the United Auto Workers union to hold an organizing vote at Tesla’s factory in Fremont, California.

On Twitter Wednesday, Musk wrote that he invited the union to hold a vote at its convenience and that Tesla would do nothing to stop it.

The UAW wouldn’t comment Thursday but spokesman Brian Rothenberg pointed out that Tesla is fighting a U.S. National Labor Relations Board ruling from last year that found the company and Musk engaged in unfair labor practices in 2018, partly because of his tweets.

The labor practices involved a UAW effort to organize the 10,000-worker Fremont plant.