U.S. customs authorities have asked cocoa traders to report where and when they encounter child labor in their supply chains in top grower Ivory Coast, three industry sources said, following calls from American lawmakers to ban some imports.

Cocoa traders and chocolate companies including Mars, Hershey, Cargill and Barry Callebaut, have repeatedly missed internationally agreed targets for reducing the worst forms of child labor from supply lines in West Africa, all sides have acknowledged.

Pressure in the United States is now increasing after two senators asked the U.S. Customs and Border Patrol (CBP) last July to use its authority to block the import of Ivorian cocoa produced with forced labor.