The email argues that the UAW’s “true allegiance is to the giant car companies” that Tesla is challenging. Musk suggests that the unionization effort is part of a battle between Tesla and “incredibly powerful” forces arrayed against its “mission to accelerate the advent of a clean, sustainable energy future.”

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The email expands on Musk and Tesla’s previous responses to allegations made by Tesla factory worker Jose Moran in a Medium post earlier this month. Moran claimed that the company demanded “excessive” mandatory overtime, leading to frequent injuries. In the Thursday email, Musk writes that the company investigated some of Moran’s claims about injury rates, and found that they were “untrue for any of the hundreds of teams in the factory.” Musk claims that the company’s injury rate was now less than half the industry average.

Musk also writes that the company has reduced overtime by hiring more workers, with overtime declining by 50% over the last year.

Moran’s post further cited below-average hourly pay as a drain on worker morale. Musk’s email argues that, with equity taken into account, a Tesla worker hired in 2013 made between $70,000 and $100,000 more over four years than an employee at other U.S. auto companies would have.

Moran argued that organizing under the UAW could be a solution to the problems he described, and the UAW later said it would welcome the role, while denying Musk’s claim that Moran was a paid organizer for the union. Musk’s latest email, however, seems to hold to claims about a strong link between Moran and the UAW, equating Moran’s claims with UAW organizing “tactics,” which Musk writes “are disingenuous or outright false.”