The Department of Justice has expanded its investigation into rising beef prices to include Teight of the largest grocery retailers in the United States, widening the federal inquiry beyond meatpacking companies and into the retail side of the supply chain.

The DOJ’s Antitrust Division sent letters to Kroger, Publix, Walmart, Albertsons, Aldi, Ahold Delhaize USA, Costco and Amazon regarding recent increases in retail beef prices. The department is seeking information about beef sales, pricing, costs, profit margins and purchasing practices.

The expansion follows a May investigation into the nation’s four largest beef processors, JBS, Cargill, Tyson Foods and National Beef, which collectively control more than 85% of the U.S. beef processing market. Federal officials are examining whether the industry’s high level of consolidation and other practices have contributed to higher prices for consumers and squeezed cattle producers.

Attorney General Todd Blanche has said the department has reviewed more than 3 million documents and interviewed participants in the beef industry as part of the investigation. The DOJ has also encouraged whistleblowers to provide information about possible antitrust violations.

The investigation comes as American consumers face historically high beef prices while the domestic cattle herd remains near its lowest level in decades. Ground beef averaged $6.89 per pound in July, according to data cited by the Washington Examiner, up roughly 10% from a year earlier.

President Donald Trump has made lowering food prices and addressing consolidation in the meat industry a priority. Last week, he announced plans to allow farmers and ranchers greater ability to process their own meat, arguing that the policy could help break the power of large meat processors.

The expanded DOJ investigation does not indicate that any of the eight retailers have violated antitrust laws. The companies are being asked to provide information as federal investigators determine whether unlawful pricing or other anticompetitive practices have contributed to elevated beef costs.