Tesla's assembly factory in Fremont, California, remains a target for the United Auto Workers union ahead of the start of Tesla Model 3 production next year. The factory, with more than 3,000 employees, is the only assembly plant in the United States owned by an American automaker that's not represented by the UAW.

Workers assemble the Model S at the Tesla Factory in Fremont

UAW President Dennis Williams told USA Today: "We just believe workers ought to have a voice in the workplace, and they ought to have collective bargaining rights" and that the UAW is "not approaching this in an adversarial way." Williams has also met with Tesla CEO Elon Musk, though wouldn't comment on whether or not they had discussed unionization of the factory.

The Tesla Factory in Fremont was formerly known as NUMMI, a joint venture between GM and Toyota producing vehicles like the Toyota Matrix and Pontiac Vibe. The plant, which had produced a peak of 500,000 vehicles a year, was shuttered in 2010 and re-opened under Tesla's banner later in the year.

Tesla currently is on track to produce a combined 90,000 Model S sedans and Model X SUVs at the Fremont facility by the end of the year, but is publicly aiming to hit 500,000 vehicles annually by the end of 2018. That will be aided tremendously by the launch of the Model 3 — Tesla plans to produce up to 200,000 of the $35,000, 215-mile-range EV by the end of 2017 and has more than 373,000 reservations on file for the car.