By JEFF AMYJACKSON, Miss. (AP) â¿¿ Pro-union workers said Tuesday that Nissan Motor Co. has threatened to close its Canton, Miss. assembly plant if workers vote for the United Auto Workers to represent them, though the company denies such threats. Such threats would violate federal law, which bars managers from telling employees they'll close a plant in retaliation for a pro-union vote. "I think the UAW's allegation that we've threatened and intimidated our Canton employees is simply not truthful," spokesman David Reuter said. "Nissan follows the law and always has." Union supporters, aided by prominent black ministers and actor Danny Glover, held a rally Tuesday at Tougaloo College to criticize the company. The UAW has been trying to unionize the 5,200-worker plant for years, but no petition for an election has been filed. In the meantime, the union is trying to push the Japanese automaker to allow it inside the plant to present its case to workers, saying Nissan is running an unfair anti-union campaign. American unions have increasingly focused on such calls for fairness or company neutrality in union elections as they struggle to stanch member losses. Morris Mock, a Pearl resident who works at Nissan, said that in group meetings, company managers implied the factory might close. However, he said that a manager was more direct in a one-on-one meeting, saying "They're going to move this factory away." "In the one-on-ones, they can say it," Mock said. It's just their word against mine." If the allegations were true, Reuter asked, why hasn't a UAW supporter filed a complaint with the National Labor Relations Board? That body is charged with enforcing federal labor law. Kathleen McKinney, the director of the NLRB's New Orleans office, said the board received two unfair labor practice complaints in late summer. Neither of them dealt with a threat of closing the plant. McKinney said both complaints were investigated and dismissed in September after the board found no proof. No other complaints are pending.