In a post on Medium published Thursday, a Tesla employee claimed that many workers at the company’s Fremont, Calif. factory have been “talking about unionizing, and have reached out to the United Auto Workers for support.”

The employee, Jose Moran, makes a number of allegations about the working conditions there, including lower-than-average pay, excessive mandatory overtime, low morale, unfair promotions, high turnover, and frequent workplace injuries. Bloomberg News initially reported the story.

“We need better organization in the plant, and I, along with many of my coworkers, believe we can achieve that by coming together and forming a union,” Moran wrote.

“Just as CEO Elon Musk is a respected champion for green energy and innovation, I hope he can also become a champion for his employees.”

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Moran said in his post that early talk of unionizing has gotten Tesla’s attention.

The company has begun to respond. In November, they offered a raise to employees’ base pay — the first we’ve seen in a very long time.

But at the same time, management actions are feeding workers’ fears about speaking out. Recently, every worker was required to sign a confidentiality policy that threatens consequences if we exercise our right to speak out about wages and working conditions. Thankfully, five members of the California State Assembly have written a letter to Tesla questioning the policy and calling for a retraction.

But Tesla has seen similar unionizing efforts before, the company responded in a statement emailed to Fortune on Thursday:

“As California’s largest manufacturing employer and a company that has created thousands of quality jobs here in the Bay Area, this is not the first time we have been the target of a professional union organizing effort such as this.

The safety and job satisfaction of our employees here at Tesla has always been extremely important to us. We have a long history of engaging directly with our employees on the issues that matter to them, and we will continue to do so because it’s the right thing to do.”

Tesla CEO Elon Musk also weighed in via a series of direct messages on Twitter with tech publication Gizmodo.

“There is sometimes mandatory overtime if we are trying to make up for a production stoppage, but it is dropping almost every week,” he reportedly wrote.

Musk countered the claims made by the employee, at one point even alleging that the employee “doesn’t really work for us”; he “was paid by the UAW to join Tesla and agitate for a union.”

“Frankly, I find this attack to be morally outrageous,” Musk wrote.

Efforts to unionize would threaten to disrupt Tesla as it prepares its factory for its most important endeavor yet: the $35,000 mass-market Model 3.