Rep. John Moolenaar, chairman of the House Select Committee on China, urged Secretary of State Marco Rubio and other senior U.S. officials to scrutinize South Korea’s expanding economic, technological and diplomatic engagement with China. In a letter, Moolenaar said the unprecedented pace of high-level exchanges, including Chinese President Xi Jinping’s visit to South Korea followed by President Lee Jae-myung’s trip to China, could develop beyond an allied policy dispute into a structural realignment. He said Xi’s references to shared sacrifice against Japanese militarism risked fracturing U.S.-South Korea-Japan coordination and argued that Lee’s past comment questioning the relevance of a Taiwan Strait conflict suggested Seoul might not support a regional response to Chinese military action. Moolenaar also warned that South Korean semiconductor facilities in Xi’an, Wuxi and Dalian could give Beijing leverage over critical U.S. supply chains. He alleged that South Korean regulators treated Chinese platforms such as AliExpress and Temu more leniently than U.S. companies including Coupang, citing 11 agencies and penalties totaling $409 million in the Coupang case. The letter follows broader friction over alliance policy, U.S. Forces Korea operations, intelligence sharing and Seoul’s engagement with Beijing. Moolenaar requested a State Department briefing by the end of next month, while South Korea’s Foreign Ministry reaffirmed the alliance as the cornerstone of its foreign policy and said regulations apply equally to companies of all nationalities.