WASHINGTON—Surging enforcement by Customs and Border Protection officers of import bans on products made from forced labor is producing disputes over halted cargo and complaints from importers about the delays and a lack of transparency.

Enforcement has accelerated over the past year, according to customs data, as Washington issued multiple orders banning cotton and tomato products and other items from China’s Xinjiang region, where the government is conducting mass detentions of Uyghurs and other largely Muslim ethnic groups.

Caught in the sweep are apparel companies like retailer Uniqlo Co.—which had a shipment of men’s shirts stopped early this year—and other importers of cotton products, which have to show that their often multilayered supply chains are free from forced labor. Importers have three months from the time a shipment is detained to prove the products are clean, under rules that trade lawyers and business groups said require a high burden of proof. Otherwise, the cargoes must be exported or abandoned.

“I have heard anecdotally that some shipments have been released but most have been either denied or have not been decided,” said Richard Mojica, a trade lawyer with Miller & Chevalier in Washington, D.C.

Trade lawyers and business groups expect more import bans and disputed shipments to come as Washington puts more emphasis on human rights in its intensifying rivalry with Beijing and CBP steps up enforcement.