A former Bill Heard Enterprises worker in Las Vegas has filed suit in Alabama claiming that the nation’s largest chain of Chevrolet dealerships violated federal labor law when it fired thousands of employees last month. Bill Heard, based in Columbus, Ga., sought bankruptcy protection on Sept. 28 after shuttering all its remaining dealerships, including one in Plant City. Edward Kratzel’s lawsuit against Bill Heard and about two dozen affiliated companies claims they violated employees’ rights under the Worker Adjustment and Retraining Notification Act. The act says companies must give at least 60 days’ advance written notice of firings and continue to pay certain wages, salary and benefits during the notice period. “It’s time for ‘Mr. Big Volume,’ as Mr. Heard called himself, to ensure that his employees survive this transition in accordance with the law,” said Kratzel’s lawyer, Jack A. Raisner of New York.