<h1>South Korean president warns firms may curb U.S. investment unless U.S. fixes visa rules after mass worker detentions</h1> The South Korean president warned that South Korean companies will likely hesitate to maintain or make direct investments in the United States unless the U.S. improves its visa system for Korean workers, after more than 300 South Korean workers were detained following an immigration raid at a battery factory under construction at a major automaker's U.S. plant; officials said those workers are to be repatriated by charter flight. Seoul and Washington are discussing visa-system changes, and the president said a system permitting skilled Korean workers to be sent to industrial sites would substantially influence future South Korean investment decisions in the U.S.