The United Auto Workers union has waged a long and mostly futile campaign to organize factories in the South, where much of the nation’s auto production has shifted. Now the union sees a breakthrough in sight.

On Tuesday, the U.A.W. said a petition for a union election had been filed by employees at a Nissan plant in Mississippi with more than 6,000 workers. They asked for a vote within a month.

A victory at the plant, which the U.A.W. has been working hard to unionize since 2012, would be a major prize in a traditionally hostile region. The effort comes almost three and a half years after the union’s last high-profile election at a so-called foreign transplant facility, a Volkswagen plant in Chattanooga, Tenn., ended in a narrow defeat.

Union officials announced the organizing milestone at a news conference near the Nissan plant in Canton, Miss. In a statement, the U.A.W. cited “a pattern of labor abuses by Nissan against its predominantly African-American work force in Mississippi” and said the plant was “one of only three Nissan facilities in the world” that lack a union.