The lawsuit, filed in a Chicago court, alleged that the deal would remove competition and raise costs for farmers, Bloomberg reported.
Deere, which is the world's largest maker of agricultural machinery, agreed to buy the unit from Monsanto in November 2015. The terms of the deal were not disclosed at the time, but the lawsuit said Deere agreed to pay $190 million for the Monsanto unit.
Precision Planting would give farmers and Deere's equipment real-time planting data through Monsanto's FieldView app.
Shares of both companies fell by about 2% to session lows in trading. Shares of other agricultural companies including Dow Chemical, DuPont, and Syngenta also slipped on the news.
Business Insider has reached out to Deere and Monsanto for comment.