South Korea’s customs authority on Wednesday warned exporters that products recognized as Korean under the Korea-U.S. Free Trade Agreement (KORUS FTA) may still face U.S. tariffs due to stricter American rules of origin. The Korea Customs Service (KCS) released new guidance to help companies understand how the U.S. determines product origin under Section 232 of its Trade Expansion Act, which allows for tariffs based on national security concerns.

The announcement comes as the U.S. expands its list of tariffed items. On Monday, Washington added refrigerators, washing machines and other home appliances to its Section 232 measures, bringing the total number of affected products to 30. The tariffs apply to goods made with steel or aluminum if those metals make up more than half of the product and more than 10% of the input value comes from a third country. That means some South Korean-made goods may still be hit with U.S. tariffs even if they qualify as Korean under KORUS FTA rules.