The Federal Trade Commission sued to block a proposed merger between grocery giants Kroger and Albertsons, the parent company of Shaw’s, saying the $24.6 billion deal would eliminate competition and lead to higher prices for millions of Americans.

The FTC filed an administrative complaint against the companies Monday, which will be considered by an administrative law judge at the agency. It also filed a lawsuit with the U.S. District Court in Oregon requesting a temporary injunction blocking the merger. That lawsuit was joined by the attorneys general of eight states and the District of Columbia.

Kroger and Albertsons, two of the nation’s largest grocers, agreed to merge in October 2022. The deal would be the biggest grocery merger in US history, according to the FTC.

The companies said a merger would help them better compete with Walmart, Amazon, Costco and other big rivals. Together, Kroger and Albertsons would control around 13% of the U.S. grocery market; Walmart controls 22%, according to J.P. Morgan analyst Ken Goldman.

Both companies, immediately after the FTC announcement, said that they will challenge the agency in court.

Kroger, based in Cincinnati, Ohio, operates 2,750 stores in 35 states and the District of Columbia, including brands like Ralphs, Smith’s and Harris Teeter. Albertsons, based in Boise, Idaho, operates 2,273 stores in 34 states, including brands like Safeway, Jewel Osco and Shaw’s. Together the companies employ around 700,000 people.

But the merger, announced at a time of high food-price inflation, was bound to get tough regulatory scrutiny. U.S. prices for food eaten at home typically rise 2.5% per year, but in 2022 they rose 11.4% and in 2023 they rose another 5%, according to government data. Inflation is cooling, but gradually.

“Kroger’s acquisition of Albertsons would lead to additional grocery price hikes for everyday goods, further exacerbating the financial strain consumers across the country face today,” Henry Liu, the director of the FTC’s Bureau of Competition, said in a statement.

The Biden administration has also shown a willingness to challenge big mergers in court. Last year, the Justice Department sued to block a proposed merger between JetBlue Airways and Spirit Airlines. A federal judge agreed with the administration and blocked the merger last month. The airlines have appealed.

The White House didn’t comment Monday, saying it doesn’t weigh in on pending litigation. But Jon Donenberg, deputy director of President Biden’s National Economic Council, said that Biden supports “fair and vigorous antitrust enforcement.”

“When large corporations are not checked by healthy competition, they too often do not pass cost savings on to consumers and exploit their workers,” Donenberg said.