U.S. Customs officials say people entering the U.S. from Mexico will have to leave behind a favorite snack starting Thursday — pork rinds, or chicharrones as they're called south of the border.

The salty slices of deep-fried pork skin often seasoned with chili powder will be seized by customs inspectors unless carriers produce a certificate issued by the national government where the snacks originated.

The new rules come as the U.S. Department of Agriculture keeps an eye out for produce that could carry threats to U.S. agriculture. A U.S. Customs spokesman said insufficiently cooked pork rinds could carry classical swine fever, also known as hog cholera, an illness that affects pigs.

Previously pork rinds were cleared if they passed a crispness test, crumbling in an inspector's hands when bent. Now only pork rinds from a few states in southern and western Mexico will be cleared on that test.