Workers at all of Kellogg's U.S. plants went on strike Tuesday.

The cereal maker has plants in Omaha, Nebraska; Battle Creek, Michigan; Lancaster, Pennsylvania; and Memphis, Tennessee.

Union workers are upset over pay and benefits, according to The Associated Press. A spokesperson for one of the local unions in Omaha told the Associated Press that the company has also threatened to move some jobs to Mexico.

A spokesperson for Kellogg's said it's disappointed in the union workers' decision to strike.

"Kellogg provides compensation and benefits for our U.S. ready to eat cereal employees that are among the industry’s best," a company spokesperson told The Associated Press.

Kellogg's reportedly plans on speaking with union workers to try and resolve their differences.

In the meantime, the company is working on contingency plans to limit disruptions to its supply.