Deere & Co. is being sued by U.S. antitrust officials seeking to block its purchase of Monsanto Co.’s Precision Planting LLC equipment business, a deal the government says would eliminate competition and raise costs for farmers.

Deere’s acquisition would combine the only two significant U.S. providers of high-speed precision planting systems used by farms, giving the company control of close to 90 percent of the U.S. market, the Justice Department said Wednesday in a complaint filed in federal court in Chicago.

“If this deal were allowed to proceed, Deere would dominate the market for high-speed precision planting systems and be able to raise prices and slow innovation at the expense of American farmers who rely on these systems,” said Renata Hesse, the head of the antitrust division.

Deere, the world’s largest maker of agricultural machinery agreed to buy the Monsanto unit in November for $190 million, according to the complaint, as it works to make its machines more technologically advanced and boost farmer productivity.

Both companies said they would contest the lawsuit, arguing the combination will benefit farmers. The U.S. allegations are “misguided,” Deere said in a statement. “Competition in precision agriculture is strong and growing in all of these channels.”

 Approximately 75 percent of the global crop-chemicals industry could end up in the hands of three companies with pending deals between Dow Chemical Co. and DuPont Co., China National Chemical Corp. and Syngenta AG and a possible tie-up between Monsanto and Bayer AG.