Union workers at Mack Trucks have voted down a tentative five-year contract agreement reached with the company and plan to strike at 7 a.m. Monday, the United Auto Workers union says.

Union president Shawn Fain said in a letter to Mack parent company Volvo Trucks that 73 per cent of workers voted against the deal in results counted on Sunday.

The UAW represents about 4,000 Mack workers in three states. Union leaders had reached a tentative agreement on the deal on Oct. 1.