Attorneys general for 35 states filed suit Thursday against the makers of the Suboxone, a drug used to treat opioid addiction, alleging they schemed to stall the entry of a generic form of the drug into the market.

The states accuse Reckitt Benckiser Pharmaceuticals and Indivior of conspiring with MonoSol Rx to switch Suboxone from a tablet to a dissolving film before the drug’s exclusivity period barring generic competition was up, according to the complaint filed in U.S. District Court for the Eastern District of Pennsylvania. This delay tactic ran afoul of state and federal antitrust laws, the states’ attorneys said.