McDonald’s has been sued in a US federal court in a proposed nationwide class action that accuses the fast-food giant of using AI to fix menu prices.

The lawsuit was filed on Friday in Chicago. It alleges McDonald’s illegally coordinates prices across its franchises and company-owned restaurants through an AI-powered pricing system trained on nonpublic data.

The complaint says McDonald’s violated US antitrust law by conspiring with independent franchisees to fix prices. It claims the company has enforced a coercive price-fixing agreement since 2019. The plaintiffs seek to represent a class of potentially millions of McDonald’s customers.

Reuters reported last week that McDonald’s pricing engine uses machine-learning algorithms to analyse data from millions of daily transactions across its nearly 14,000 restaurants.

McDonald’s called the allegations speculative and uninformed on Monday. The company said AI does not set the price of a Big Mac. It said franchisees make their own pricing decisions and that pricing recommendation tools are widespread across industries.