Hundreds of union employees at three U.S. Nabisco bakeries that make Oreo and Chips Ahoy cookies and Ritz Crackers have gone on strike to protest proposed changes amid contract negotiations with parent company Mondelez International, Inc.

Approximately 200 workers at a factory in Portland, Oregon, have been on strike for two weeks and were joined on Monday by about 400 employees at Nabisco's bakery in Richmond, Virginia. On Thursday, workers at Nabisco's bakery in Chicago also walked off the job to go on strike.

Employees at a sales distribution center in Aurora, Colorado, also joined the strike on Aug. 12. All of the workers on strike are members of the Bakery, Confectionery, Tobacco Workers, and Grain Millers International Union, which announced the Chicago strike on Thursday.

"This fight is about maintaining what we already have," Mike Burlingham, vice president of BCTGM Local 364 in Portland, told TODAY Food. "During the pandemic, we all were putting in a lot of hours, demand was higher, people were at home, and the snack food industry did phenomenally well.

"Mondelez made record profits and they want to thank us by closing two of the U.S. bakeries (last month) and telling the rest of us we have to take concessions, what kind of thanks is that? We make them a lot of money. It's very disheartening. How is that supposed to make us feel?"

The union is in the midst of negotiating a new four-year contract with Mondelez after the previous one expired in May.

Union leaders say that Mondelez has proposed switching from eight-hour shifts, five days a week, to 12-hour shifts, three or four days a week, without overtime, and with increased mandatory work on weekends without extra pay.