CHICAGO, Oct. 9 (Xinhua) -- Union workers at Volvo Group-owned Mack Trucks went on strike Monday after a majority of the company's union members in Pennsylvania, Maryland and Florida rejected a tentative agreement Sunday.

Covering 4,000 unionized workers, the tentative agreement differs based on location and job. For many Mack employees, it included about a 19-percent wage increase, a 3,500-U.S. dollar ratification bonus and an increased 401(k) contribution. It reduced the length of time to the top wage by one year to five years.

But the tentative agreement doesn't include reinstating pensions, a cost-of-living adjustment or a shorter workweek.

The United Auto Workers (UAW) representing Mack workers in the three U.S. states reached this tentative agreement with Mack Trucks on Oct. 1.

In a letter to Volvo Trucks, the parent company of Mack Trucks, UAW President Shawn Fain said UAW members and workers across the country are seeking their fair share in wages and benefits.

"I'm inspired to see UAW members at Mack Trucks holding out for a better deal, and ready to stand up and walk off the job to win it," Fain was quoted by The Detroit News as saying in the letter. "The members have the final say, and it's their solidarity and organization that will win a fair contract at Mack."

In response, Mack Trucks President Stephen Roy said in a statement Sunday night that the company is "surprised and disappointed" that the union chose to strike.

Mack is part of the only heavy truck manufacturing group that assembles all of its vehicles and engines for North America in the United States, competing against trucks built in lower-cost countries, said the statement.

The company is committed to collective bargaining and is confident both sides will reach a deal that delivers competitive wages and benefits while safeguarding the company's future, it said.