The United Automobile Workers union on Friday said it had been approached by workers at Tesla Inc's Fremont, California, assembly plant, rejecting a charge by the chief executive of the luxury electric car maker that a worker who publicly criticized the company was on the UAW payroll.

The nascent move to organize at Tesla's factory shines an unwelcome spotlight on allegations of long hours, mandatory overtime and preventable injuries at a time when Tesla is accelerating production to meet ambitious targets.

The worker, 43-year-old Jose Moran, said on Friday his goal was to unionize at the factory where he has worked since 2012, often pulling 12-hour days, six days a week.

"A lot of workers believe we have a right for union representation and a right to represent ourselves and our own interest. We don't believe the company is doing that for us," Moran told reporters during a conference call.

Earlier in the day, the UAW said Moran had never been paid by the union.

"We can confirm that Mr. Moran and others at Tesla have approached the UAW and we welcome them with open arms," the union said.

The Fremont factory was once a UAW-represented operation, owned by General Motors Co, but became non-union when Tesla took over in 2010.

Tesla's chief executive, Elon Musk, told the website Gizmodo on Thursday that Moran 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."

Moran said he had been congratulated by fellow factory workers since publishing a blog earlier this week citing preventable injuries at the plant, mandatory overtime and workers being paid less than the auto industry average.

"A lot of people have been ... shaking my hand, congratulating me. Glad that someone spoke up," said Moran, whose team works on Tesla's Model S sedan.

The attempts to organize comes as Tesla plans to idle the factory for a week this month to prepare for production of the high-volume Model 3 sedan. Tesla already builds Model S sedans and Model X SUVs at the plant.

Musk is pushing to launch Model 3 production by July. He has projected output will reach 500,000 vehicles a year by 2018, roughly five times last year's production.

In a video posted to the "Fair Future at Tesla" Facebook page on Friday, Moran says employees "spend more time at work than at home," and they do not feel they can report health and safety issues. "Tesla workers are fed up," he said.

About 200 Tesla workers are on the Facebook site with "more support every day," Moran told reporters.

A Tesla spokesman did not return a call for comment.

Moran's blog charged that Tesla managers required workers to sign confidentiality agreements agreeing not to speak out about wages or working conditions.

Musk, in comments reported by Gizmodo, said there is sometimes mandatory overtime, but it is tapering off.

He said Tesla's starting wages are higher than UAW starting pay and employees also receive stock grants. Confidentiality agreements are meant to prevent company secrets from leaking, Musk said.