The U.S. Justice Department is investigating crypto predictions-betting platform Polymarket for allegedly accepting trades from US-based users, according to a person familiar with the matter.

The Federal Bureau of Investigation executed a search warrant on Shayne Coplan, Polymarket’s chief executive officer, and seized his phone and electronics, according to the person who asked for anonymity to discuss non-public matters.

Under an agreement with the Commodity Futures Trading Commission reached in 2022, Polymarket is to prevent US-based traders from making transactions on the platform.