MACUNGIE, Penn. – Negotiations to end a strike by some 3,500 hourly workers at six Mack Truck plants in the U.S. were expected to resume Monday.

The workers began their stoppage Oct. 12 after their contracts expired Oct. 1, CNBC reported. The network said the United Auto Workers gave the go-ahead for the strike after failing to secure a deal.

It is the first UAW strike at Mack in 35 years.

“We are disappointed that the company failed to provide any substantial offer prior to the Oct. 1st expiration date or during the subsequent meetings held during the period in which we extended the contract,” CNBC quoted UAW secretary-treasurer Ray Curry as saying.

Wages, shift premium and holiday schedules are among sticking points in the negotiations. Facilities in Pennsylvania, Maryland and Florida are affected by the strike, the company said.

In a statement posted on the Mack Trucks website, company president Martin Weissburg said he was “surprised and disappointed that the UAW decided to strike rather than to allow our employees to keep building trucks and engines while the parties continued to negotiate.”

He also reiterated the company’s commitment to the collective bargaining process.

Mack Trucks is a division of AB Volvo.