OMAHA, Neb. (AP) — Work at all of the Kellogg Company’s U.S. cereal plants came to a halt Tuesday as roughly 1,400 workers went on strike, but it wasn’t immediately clear how much the supply of Frosted Flakes or any of the company’s other iconic brands would be disrupted.

The strike includes plants in Omaha, Nebraska; Battle Creek, Michigan; Lancaster, Pennsylvania; and Memphis, Tennessee.

The union and the Battle Creek-based company have been at an impasse at the bargaining table for more than a year, said Daniel Osborn, president of the local union in Omaha. The dispute involves an assortment of pay and benefit issues such as the loss of premium health care, holiday and vacation pay and reduced retirement benefits

“The company continues to threaten to send additional jobs to Mexico if workers do not accept outrageous proposals that take away protections that workers have had for decades,” said Anthony Shelton, president of the Bakery, Confectionary, Tobacco Workers and Grain Millers International Union.

The threat to move work to Mexico doesn’t sit well with Osborn.

“A lot of Americans probably don’t have too much issue with the Nike or Under Armor hats being made elsewhere or even our vehicles, but when they start manufacturing our food down where they are out of the FDA control and OSHA control, I have a huge problem with that,” Osborn said.

The company insists that its offer is fair and would increase wages and benefits for its employees, who it said made an average of $120,000 a year last year.

“We are disappointed by the union’s decision to strike. Kellogg provides compensation and benefits for our U.S. ready to eat cereal employees that are among the industry’s best,” Kellogg spokesperson Kris Bahner said in a statement.

Osborn said he expects the company to try to bring non-union workers into the plants at some point this week to try to resume operations and maintain the supply of its products.

The company acknowledged that it is “implementing contingency plans” to limit supply disruptions for consumers.

The plants have all continued to operate throughout the coronavirus pandemic, but Osborn said that for much of that time workers were putting in 12-hour shifts, seven days a week to keep up production while so many people were out because of the virus.

“The level we were working at is unsustainable,” Osborn said.

Kellogg’s workers aren’t the first food workers to strike during the pandemic.

Earlier this summer, more than 600 workers at a Frito-Lay plant in Topeka, Kansas, walked off the job to protest working conditions during the pandemic, including forced overtime. That strike ended in July when workers ratified a new contract.

Workers at Nabisco plants in five states went on strike in August to protest plans by Nabisco’s parent, Mondelez International, to move some work to Mexico, among other issues, according to the Bakery, Confectionary, Tobacco Workers and Grain Millers International Union, which also represents the Kellogg’s workers. That strike ended last month when workers ratified a new contract.