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

The FTC filed a lawsuit in U.S. District Court in Oregon on Monday. It was joined in the suit 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 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.