A vehicle parts supplier for South Korean automaker Hyundai's assembly line in Montgomery, Alabama, was accused of using underage migrant labor, citing the minors' families, multiple factory employees, and police sources, in a Reuters investigation published on Friday.

According to one former employee, she worked "alongside about a dozen minors on her shift" for several years before leaving the Hyundai subsidiary for another plant. According to another source, there could have been up to 50 underage workers across different shifts, mostly migrants and some as young as 12.

The factory at the center of the scandal is SMART Alabama LLC, an auto parts manufacturer in Luverne, Alabama, that produces stamped metal parts for Hyundai's largest US-based assembly plant in nearby Montgomery.

The controversy began when a 13-year-old Guatemalan migrant child went missing from her family's home in Alabama in February, prompting an AMBER alert (Missing Person Alert). Her father and police officers who assisted in the search for the child told Reuters that she and her two brothers, ages 12 and 15, all worked at the plant. The girl had fled with a 21-year-old colleague, also a Guatemalan migrant who had been deported, to "look for other work opportunities."

Read next: Cadbury faces child labor claims on its cocoa farms

SMART is said to have fired all of its underage workers amid increased police and media scrutiny over the girl's disappearance. Reuters' investigation was unable to confirm the exact number of alleged child laborers, their employment terms, or working conditions. Local police claim they do not have the authority to investigate labor law violations, but they have notified the state attorney general's office of their findings.

Hyundai issued a statement on Friday in response to the damning allegations, claiming that the company "does not tolerate illegal employment practices at any Hyundai entity" and that it has "policies and procedures in place that require compliance with all local, state, and federal laws."

SMART, for its part, denied "any allegation that it knowingly employed anyone who is ineligible for employment," and pointed the finger at the staffing agencies it relies on to fill jobs, saying it expects them to "follow the law in recruiting, hiring, and placing workers on its premises."