Nike Inc. has filed a lawsuit against Boris Berian, a top contender for the U.S. Olympic Team in the 800 meters, to prevent him from wearing New Balance merchandise at upcoming high-profile events.

Nike claims Berian would be violating his endorsement contract. Berian has said on Twitter that the Nike deal ended in December. The news was first reported by The Oregonian.

Nike claimed it had a right to match any offers after the deal expired and that it had matched New Balance’s offer. The suit seeks to bar Berian, the fifth-fastest American time in the 800, from wearing New Balance footwear and apparel while the case proceeds. Upcoming events include the Olympic Trials and possibly the Olympics.

Nike filed its lawsuit in U.S. District Court in Portland in March.