Monsanto Co. was sued on behalf of shareholders over claims its chief executive and board members stand to improperly profit from a planned acquisition by Bayer AG.

An investor alleges Monsanto Chief Executive Officer Hugh Grant stands to collect $18 million in cash and benefits, and that directors would similarly benefit from the merger. Grant and board members suffer conflicts of interest and have withheld information from investors in a bid to pursue the deal, according to the complaint.

Monsanto believes the claims asserted in the lawsuit are without merit, company spokeswoman Sara Miller said Tuesday in an e-mail.

The offer for St. Louis-based Monsanto will be financed with a combination of debt and equity but investors have been wary. The two companies will need regulatory approval for the deal in more than 30 jurisdictions, and Bayer doesn’t expect to complete the transaction until the end of next year.