DETROIT, Oct 19 (Reuters) - Hyundai Motor Co (005380.KS), Korea's top automaker, is investigating child labor violations in its U.S. supply chain and plans to "sever ties" with Hyundai suppliers in Alabama found to have relied on underage workers, the company's global chief operating officer Jose Munoz told Reuters on Wednesday.In addition, Munoz told Reuters he had ordered a broader investigation into Hyundai's entire network of U.S. auto parts suppliers for potential labor law violations and "to ensure compliance."Munoz's comments represent the Korean automotive giant's most substantive public acknowledgment to date that child labor violations may have occurred in its U.S. supply chain, a network of dozens of mostly Korean-owned auto-parts plants that supply Hyundai's massive vehicle assembly plant in Montgomery, Alabama.Munoz did not offer further detail into how long Hyundai's probe of its U.S. supply chain would take, when Hyundai or any partner plants could end their dependence on third party staffing firms for labor, or when Hyundai could end commercial relationships with two existing Alabama suppliers investigated for child labor violations by U.S. authorities.Munoz's comments come on the same day that an investor group working with union pension funds sent a letter to Hyundai, pushing it to respond to reports of child labor at U.S. parts suppliers, and warning of potential reputational damage to the Korean automaker."