Regulators filed a lawsuit Monday to block the world's largest beef processor from buying the nation's fourth-largest operation, saying such a deal could push up beef prices for consumers and drive down prices paid to ranchers and feedlots.

The Department of Justice and attorneys general for 13 states filed the suit against Brazilian beef producer JBS S.A. and National Beef Packing Co. of Kansas City, Mo.

In March, JBS had said it would acquire National Beef in a $560 million stock-and-cash deal, which would make it the nation's largest beef processor. It also announced a deal to buy Smithfield Beef Group Inc., the nation's fifth-largest beef producer, for $565 million. The Department of Justice said it is not challenging that deal, only the deal with the larger player, which would combine two of the top four U.S. beef packers.

Grocers, food service companies and ultimately, consumers will likely have to pay higher prices for beef if JBS's buyout of National Beef were to go through, according to filings in U.S. District Court in the Northern District of Illinois.

The suit said the deal would put more than 80 percent of domestic fed cattle-packing capacity in the hands of three companies — JBS, Tyson Foods Inc. and Cargill Inc. Regulators estimate if JBS were allowed to buy National, it would have annual sales of more than $14 billion and the ability to slaughter more than one-third of U.S. fed cattle-packing capacity, at about 40,000 head of cattle a day.

The combination would not only lead to higher retail prices for U.S. consumers but also lower wholesale prices for cattle producers, ranchers and feedlots, the suit said.

JBS became the third-largest beef processor in the U.S. last year after purchasing Greeley, Colo.-based Swift & Co. for $225 million.

National Beef was disappointed by the lawsuit and plans to "vigorously contest" the attempt to block the deal, said Steve Hunt, chief executive of U.S. Premium Beef LLC, which is the majority owner of National Beef.

USPB's producer members voted to approve the transaction in March.

National Beef Chief Executive John R. Miller said the deal would help customers and producers by helping them save on costs.

JBS did not immediately return messages left at its U.S. headquarters Monday.

Testifying before Congress in May, the head of JBS SA's North American operations said the buyout would mean more jobs and more competition in the industry.

"We are investing billions of our company's money in the United States, with a goal to grow the industry, hire more U.S. workers, and increase demand for U.S. beef," Wesley Batista told members of the Senate Judiciary Subcommittee on Antitrust, Competition Policy and Consumer Rights.

But the lawsuit said the buyout would hurt packers because it would likely lessen competition between JBS and the other two top players to buy fed cattle and produce beef, "making interdependent or coordinated conduct among these large packers more likely."

The filing said that means producers, ranchers and feedlots will likely get lower prices for their cattle.

Sen. Herb Kohl, D-Wis., chairman of the Senate Antitrust Committee said in a statement that he would have preferred that the Smithfield portion of the deal be blocked as well, but he was glad part of it was. Sen. Tom Harkin, D-Iowa, chairman of the Senate Agriculture Committee, applauded the move but said he remained "concerned over the impacts of JBS's acquisition of Smithfield's beef division on independent cattle producers."

States involved in the suit are from the central part of the U.S. and the west and have strong meatpacking ties. They include Colorado, Kansas, Missouri, Ohio, Wyoming, Minnesota and Texas.

"Consolidation in the agricultural markets often comes at the expense of consumers and smaller farming operations, and the merger ought to be stopped," Minnesota Attorney General Lori Swanson said in a statement.