A drive by the United States to block illegal imports of goods made by forced labor has been hampered by a lack of skilled staff and reliable data, a government watchdog said in a report.

Customs and Border Protection (CBP) has in recent years suspended some investigations into imports it suspected to be tainted by slave labor because of staff shortages, the Government Accountability Office (GAO) found on Tuesday.

Under a 2016 law, it is illegal to import goods into the United States that are made entirely or in part by forced labor – which includes prison work, bonded labor and child labor.

Recent seizures by U.S. officials include rubber gloves from Malaysia and products such as cotton and clothes from Xinjiang, China. The region is home to many Muslim Uighur people – a minority that has faced mass detention in government camps.