(The Hill) — Around 4,000 union workers at Mack Trucks facilities went on strike Monday morning after rejecting a tentative contract on Sunday evening.

Striking Mack workers in Pennsylvania, Maryland and Florida are represented by the United Auto Workers, which is also actively engaged in separate negotiations with the “Big Three” Detroit automakers. 

Seventy-three percent of workers voted against the tentative deal, UAW President Shawn Fain said in a letter sent Sunday to the director of employee relations at Volvo, which owns Mack.

Mack workers walked out at 7 a.m., according to the union, upping the pressure on the automotive industry.

More than 30,000 UAW workers across 22 states are now on the picket line, the UAW said in a statement released Monday. 

“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 said in the statement.

Union leaders had reached a tentative agreement with Mack on Oct. 1 that included a 10-percent wage increase in the first year, a compounded 20-percent wage increase over the five-year contract, a $3,5000 bonus upon contract ratification and a guarantee that health insurance premiums would not increase.

But the union and the company remain at odds on issues including “wage increases, cost of living allowances (COLA), job security, wage progression, skilled trades, shift premium, holiday schedules, work schedules, health and safety, seniority, pension, 401(k), healthcare and prescription drug coverage, and overtime,” Fain wrote in the letter.

Mack Trucks said in a Sunday statement that the company was “surprised and disappointed” by the union’s decision to strike, a decision it called “unnecessary.”

The statement also emphasized that the UAW had called the tentative agreement a record for the heavy truck industry. 

“The members have the final say, and it’s their solidarity and organization that will win a fair contract at Mack,” Fain said.

Neither the UAW nor Mack Trucks returned requests for comment from The Hill.

The UAW has set expectations high in its bargaining with Ford, General Motors and Stellantis, the so-called Big Three, against which the UAW launched targeted strikes at selected facilities on Sept. 15.

The initial strikes targeted one assembly plant for each automaker. The union later expanded strikes to include 38 GM and Stellantis parts warehouses and two additional Ford and GM assembly plants.

The UAW announced Friday that it would not expand the strikes after GM agreed to bring electric vehicle facilities into the UAW contract, unionizing roles around which there had been significant uncertainty and progress with all three automakers.