A renewed effort to unionize Tesla’s (tsla) only auto plant appears to be underway.
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.”
Get Data Sheet, Fortune’s technology newsletter.
Moran said in his post that early talk of unionizing has gotten Tesla’s attention.
But Tesla has seen similar unionizing efforts before, the company responded in a statement emailed to Fortune on Thursday:
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.