The message resonated with many workers, although some found it condescending. “They were telling African-Americans look what they provided for us, but I had a job before I came to Nissan,” said David Brown, who was undecided the week before the vote but ended up supporting the union. “I had a house already, had cars already. Nissan didn’t provide me with it.”

In meetings between management and workers, and in a video featuring the plant’s top official, Nissan was more menacing, suggesting that a union would put workers’ jobs at risk.

“They’ve come out with some of the nastiest, most unprecedented attacks I’ve seen in the 20 years I’ve been doing this,” said Gary Casteel, the second-ranking official at the U.A.W. “This issue of threatening to close a facility is the worst threat you can put toward an employee.”

At one point leading up to the vote, managers delivered a slide presentation warning that in the event of a strike, most employees who walked out would not be guaranteed jobs afterward. Many workers appeared to find the presentation alarming, even though strikes are rare in the industry and replacing production workers could be difficult.

Another manager emphasized in a meeting that Nissan could decide not to automatically deduct workers’ union dues, in which case the union would end up sending workers a regular “bill.”

“It was just to deter people from joining, was what I’m getting out of it,” said Earnestine Mayes, a union supporter. “No one wants to sit there and pay that bill every week.”