About 1,400 striking workers at four Kellogg cereal plants in the U.S. have rejected a tentative agreement on a five-year contract negotiated by their union, the company said Tuesday.

The Bakery, Confectionery, Tobacco Workers and Grain Millers International Union, which represents the workers, said in a statement that its members had “overwhelmingly voted” against the agreement.

The strike began Oct. 5 and has largely revolved around the company’s two-tier compensation structure, agreed to in 2015, in which newer employees earn lower wages and receive less generous benefits than veteran workers.

According to a summary provided by the company, the new agreement would have immediately moved all employees with four or more years at Kellogg into the veteran tier.