Mondelez International and its largest union face ongoing tensions as the two begin contract negotiations on Tuesday.

Mondelez mdlz , which owns a Nabisco plant on Chicago’s Southwest Side, announced last summer that it would be firing half of the factory’s 1,200 workers and moving some production to its plant in Salinas, Mexico. Mondelez opened the Mexico plant in the latter end of 2014 and started to pick up production a year later—prompting Donald Trump to boycott Oreos. According to the Chicago Tribune, increasing production in Mexico is expected to save Mondelez about $46 million per year, allowing it to increase profit margins in North America.

The Bakery, Confectionery, Tobacco Workers, and Grain Millers International union, which represents most of the Nabisco plant workers, has been opposing the layoffs ever since they were announced. Last month, 277 workers received their 60-day notice, with more to come later this year.

Mondelez has negotiated the terms of the layoffs with two other unions that represent plant workers, but the BCTGM has refused to do so. Instead the union has filed a lawsuit and complaint with the Equal Employment Opportunity Commission, opposing the layoffs on grounds of discrimination.

We will vigorously defend against BCTGM Local 300’s allegations in both the federal court action and before the EEOC,” a Mondelez spokesperson told Fortune. “We as a company do not discriminate and these charges have no merit.”

Eight labor contracts covering 2,400 Mondelez workers are set to expire at the end of the this month, and the company has begun negotiating new terms with the union.