At least four major suppliers of Hyundai Motor Co and sister Kia Corp have employed child labor at Alabama factories in recent years, a Reuters investigation found, and state and federal agencies are probing whether kids have worked at as many as a half dozen additional manufacturers throughout the automakers’ supply chain in the southern U.S. state.

At a plant owned by Hwashin America Corp, a supplier to the two car brands in the south Alabama town of Greenville, a 14-year-old Guatemalan girl worked this May assembling auto body components, according to interviews with her father and law enforcement officials. At plants owned by Korean auto-parts maker Ajin Industrial Co, in the east Alabama town of Cusseta, a former production engineer told Reuters he worked with at least 10 minors. And six other ex-employees of Ajin said they, too, worked alongside multiple underage laborers.

In two separate statements sent by the same public relations firm, Hwashin and Ajin said their policies forbid the hiring of any worker not of legally employable age. Using identical language, both companies said they hadn’t, “to the best of our knowledge,” hired underage workers.

The employment of children at Hwashin and Ajin hasn’t been previously reported. The news follows a Reuters report in July that revealed the use of child workers, one as young as 12, by SMART Alabama LLC, a Hyundai subsidiary in the south Alabama town of Luverne. In August, the U.S. Department of Labor said that SL Alabama LLC, another Hyundai supplier and a unit of South Korea’s SL Corp, employed underage workers, including a 13-year-old, at its factory in Alexander City.