About 475 workers were arrested at a Hyundai car battery facility in Georgia on Thursday, in what the Department of Homeland Security is calling the largest single-site enforcement operation in its history.

“ICE Homeland Security Investigations, in coordination with our law enforcement partners, executed a judicial search warrant as part of an ongoing criminal investigation into allegations of unlawful employment practices and other serious federal crimes,” DHS said in a statement.

Steven Schrank, special agent in charge of Homeland Security investigations for the states of Georgia and Alabama, said at a press briefing Friday morning that “this was not an immigration operation where agents went into the premises, rounded up folks, and put them on buses,” but rather “a multi-month criminal investigation.”

The DHS said the majority of those arrested at the facility, located in Ellabell, Georgia, are South Korean nationals and will be held at an ICE detention facility in Folkston. No charges have been filed in the incident and the investigation is ongoing.

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A spokesperson for Hyundai told MSNBC that the company is “closely monitoring the situation and working to understand the specific circumstances. As of today, it is our understanding that none of those detained is directly employed by Hyundai Motor Company. We prioritize the safety and well-being of everyone working at the site and comply with all laws and regulations wherever we operate.”

In July, South Korea, one of the U.S.’s closest allies in Asia, pledged $350 billion for investments in U.S. projects. In return, President Donald Trump said he would lower tariffs for South Korea to 15% from the 25% duty he had threatened. Profits at Hyundai, a South Korean car manufacturer, have dropped since the U.S. imposed new auto tariffs.

A spokesperson for South Korea’s Foreign Ministry said after the raid that “the economic activities of our companies investing in the United States and the interests of our citizens must not be unduly violated during the course of U.S. law enforcement.”