More than 3,600 members of the United Auto Workers went on strike Sunday against Mack Truck, a subsidiary of AB Volvo, as the union’s strike against General Motors Co. continued.

The new walkout hit Mack Truck plants in Pennsylvania, Maryland and Florida. The union said it was standing up for fair pay, benefits and job protections for union members.

“UAW members get up every day and put in long, hard hours of work from designing to building Mack trucks,” said Ray Curry, Secretary-Treasurer of the UAW and Director of the Heavy Truck Department.

“UAW members carry on their shoulders the profits of Mack and they are simply asking for dignity, fair pay and job protections.”

Mack Truck executives said they were disappointed by the union’s decision to stage a walkout.

The UAW began a strike against General Motors on September 16, idling 48,000 union members.

The strike continues as the two side exchange contract proposals aimed at settling the dispute.