DuPont has filed a lawsuit againstMonsanto, claiming that Monsanto didn’t pay royalties awarded during a previous arbitration decision. It centers around “gene-gun technology used to develop herbicide-resistant soybeans,” according to the Delaware News Journal.

The lawsuit, filed in the Delaware Court of Chancery, seeks to enforce a 2012 arbitration panel decision requiring Monsanto to pay royalties on the technology known as Biolistic. DuPont claimed Monsanto made two initial payments totaling roughly $33.3 million, but then failed to meet additional royalty obligations.

A DuPont attorney told the News Journal that Monsanto failed to pay despite repeated demands, and that the company is owed “several million dollars.” A Monsanto spokeswoman said the comapny was puzzled by DuPont’s decision to sue since the matter has been “silent for two years.”