For Mississippi, landing Nissan was a coup. The 10-year-old auto plant was the state’s first, and its work force has climbed to 5,200, making Nissan the state’s second-largest private employer behind Ingalls Shipbuilding. Blake Wilson, president of the Mississippi Economic Council, the state’s chamber of commerce, praises Nissan for bringing thousands of jobs and donating millions to charities and the Canton school system.

“Across the South, the spirit of a nonunion environment has been a positive in the growth of all kinds of manufacturing,” Mr. Wilson said. “The nonunion environment has been a market edge in Southern states. But if you start seeing that change, it will certainly be a loss for the region.”

Nissan has invested $2 billion in its state-of-the-art plant, which uses 1,200 robots. The base wage for most of the plant’s workers is $23.22 an hour, making them the envy of many blue-collar workers in Mississippi.

Nonetheless, Morris Mock, a muscular paint technician, strongly backs unionization.

“We’re grateful that Nissan came to Mississippi, but as I grow older, I see that there are safety issues and ergonomic issues that need to be addressed,” said Mr. Mock, 39, who has worked at the plant since it opened. “Nissan started out one way, then things changed. We want to make sure our voices are heard.”

Many pro-union workers complain that the company does not listen to workers as much as they would like and puts injured workers back on the line too soon. Many are upset that their wages were frozen for five years and that the plant has hired hundreds of temporary workers, many of them starting around $12 an hour. Many experienced workers complain that they are relegated to night shifts because the temporary workers are often given the coveted day shifts.

“They give them the easier jobs so they won’t leave,” said Chip Wells, also a paint technician. “They’re standing next to us doing the same job, receiving less benefits and less pay. That’s not fair.”