It is legal unless the 30-year employee had a written employment contract which guaranteed him this additional compensation. In the absence of a contract, a company is free to set its own compenstion, including overtime or premium pay, policies so long as those polices are at least equal to wage and hour law: e.g. the employee is paid at least minimum wage, and gets overtime when working  more than 40 hours in a week. So long as the company complies with the law, it is otherwise free to set whatever policies it likes; and furthermore, employers can change these policies, even long-standing ones, at will, and does not need to continue to do something simply because it previously  did it for many years.