(NewsNation) — Federal agents have detained roughly 475 workers from a Hyundai plant in Ellabell, Georgia, in what officials are calling the “largest single site operation" in Homeland Security Investigations history.

The ICE-led raid at the HL-GA battery plant — part of a megasite by the South Korean auto company — was months in the making, said Steven Schrank, HSI special agent in charge.

Federal agents in tactical gear, supported by Georgia State Patrol, FBI, and DEA, entered the facility under a criminal search warrant tied to alleged unlawful employment practices on Thursday night, NewsNation local affiliate WSAV reported.

Schrank on Friday said the detainees were "illegally present in the United States, or in violation of their presence in the United States, working unlawfully."

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