The union, which lost an organizing vote at two factories last week, argued to federal officials that the automaker had violated labor laws.
The election, fiercely opposed by the state’s political leaders, was seen as a test of the United Automobile Workers’ ability to unionize factories in the South.
Southern political leaders say a win for the United Automobile Workers would threaten their economies. Activists want to strike a blow against a system they say exploits the poor.
As Tesla completes a factory in Berlin, Mercedes-Benz and Audi are introducing electric cars in bids to defend their dominance of the luxury market.