Nathan Bomey

USA TODAY

The United Auto Workers union signaled Friday that it's gathering support to unionize Tesla's assembly plant in Fremont, Calif., after someone claiming to be an employee of the automaker publicly criticized the company over factory conditions.

The UAW confirmed Friday that Tesla workers "have approached the UAW, and we welcome them with open arms."

The union said those workers included Jose Moran, who published a blogpost Thursday on a site called Medium alleging that "preventable injuries happen often," workers are forced into "excessive mandatory overtime," dissent is stifled and compensation is inadequate.

He did not provide any evidence for his claims, but his public call for the formation of a UAW chapter at the factory drew attention in automotive circles.

Tesla's factory south of San Francisco is the only assembly plant owned by an established American automaker that is not unionized. All General Motors, Ford and Fiat Chrysler plants in the USA are unionized in stark contrast to foreign automakers that have established non-union plants in the USA, many of them in the South.

UAW wants union for Tesla factory

Tesla CEO Elon Musk disputed Moran's claims in a Twitter message Thursday to tech blog Gizmodo. He wrote that mandatory overtime is limited, compensation is sufficient and the accusations are "morally outrageous."

"Our understanding is that this guy was paid by the UAW to join Tesla and agitate for a union. He doesn’t really work for us, he works for the UAW," Musk said without providing evidence.

The UAW shot back Friday: “Mr. Moran is not and has not been paid by the UAW. We would hope that Tesla would apologize to their employee, Mr. Moran, for spreading fake news about him."

Moran did not immediately respond to a USA TODAY message seeking comment Friday. A Tesla representative also did not respond to a request for comment.

The deepening divide between Tesla and the UAW could accelerate the union's attempt to organize the 5.3 million-square-foot plant. The facility was a joint operation of Toyota and GM before it was shuttered during the auto industry's crisis nearly a decade ago. Musk said Thursday that the UAW "killed" the plant and "abandoned the workers."

Organizing the Tesla plant would amount to a major victory for the UAW, which has failed repeatedly to add a foreign auto plant to its roster of unionized factories.

UAW President Dennis Williams said in May that the company remained interested in unionizing the plant, even as it long respected Tesla's status as a start-up company.

"We’re watching that very closely," Williams said. "We just believe workers ought to have a voice in the workplace, and they ought to have collective bargaining rights." He said the union was "not approaching this in an adversarial way."

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.