It makes sense that U.S. federal law forbids the importation of goods produced using forced labor. It makes less sense that a loophole virtually nullifies the rule: A product can't be blocked under the law unless the U.S. makes enough of it to meet domestic needs. In other words, as long as there's a market for the tainted item, it's free to enter.

The provision, within the Tariff Act of 1930, was intended to ensure the U.S. was supplied with exotic goods such as rubber, tea and coffee at a time when those goods were often produced on forced-labor plantations abroad.

In today's globalized economy, importers have enough choice to avoid such suppliers. But with the exemption intact, even if the U.S. has evidence an incoming shipment contains tainted products, it generally has no reason to act.

Congress has an opportunity to update the law as it considers the reauthorization of the U.S. Customs and Border Protection agency and the U.S. Immigration and Customs Enforcement agency. A five-year authorization bill proposed by Senate Finance Chairman Max Baucus and ranking member Orrin Hatch would remove the loophole.

If the bill passes and the amendment survives, as it should, customs would then be able to hold or reject, for instance, a shipment of clothing containing Uzbek cotton. Each year, the government of Uzbekistan, the world's third largest cotton exporter, forces schoolchildren into the fields to bring in the harvest. Because the U.S. grows plenty of cotton, Uzbek cotton produced this way arguably can't enter the U.S. legally. However, garments containing the cotton can, since Americans import more than 97 percent of what they wear.

Cashews, which aren't grown commercially in the U.S., are another import an empowered customs could target. The U.S.'s top supplier is Vietnam. Part of Vietnam's output comes from government centers where alleged drug users are confined without due process and forced to process the nuts, which are then sold to private companies for export.

Cocoa, which in the U.S. is cultivated only in Hawaii, is another item to watch. In Cote d'Ivoire, the world's leading supplier of cocoa, the use offorced child labor in the industry has been widely reported. Since 2001, major chocolate companies have vowed to make their cocoa child-labor free but keep delaying the deadline.

If the Tariff Act were stripped of its antiquated exception, U.S. consumers wouldn't have to rely on the promises of corporate executives to keep their markets free of goods corrupted by slave labor. They could rely on the law.

(Lisa Beyer is a member of the Bloomberg View editorial board.)