McDonald’s says Cargill, JBS, Tyson and National Beef secretly worked together over the past decade to limit supplies of cattle and fix prices, according to a federal lawsuit filed this month. Those Big Four meatpackers collectively control 85% of the beef industry in the U.S.

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While McDonald's customers have been complaining about having to shell out more money for their favorite menu items in recent months, the fast food chain has its own beef with meat industry prices. According to the Associated Press,

The chain accused the companies of anticompetitive measures, such as collectively limiting supply, to boost prices

McDonald's has filed a lawsuit against the nation's largest meat packers—Tyson, JBS, Cargill, and National Beef—accusing them of conspiring to fix beef prices by limiting supply to inflate costs.

McDonald's states that in early 2015, beef prices started to change "without any credible, non-collusive explanation."

In May, as McDonald’s continued to swat down lingering rumors that the chain was asking an exorbitant $18 for a Big Mac meal at locations across the country, company president Joe Erlinger wrote an open letter to Golden Arches customers,

This collusion caused the beef market to become “a monopoly in which direct purchasers were forced to buy at prices dictated by (the meat packers),” McDonald’s suit reads — later noting that the injury it has sustained as one of those buyers is what “antitrust laws were designed to prevent.”

McDonald’s has sued JBS, Tyson Foods and other leading meat processing and packing companies for allegedly conspiring for years to limit beef supplies, boosting their profits while causing the fast food giant to pay artificially higher prices.