Federal immigration authorities detained 475 people in a raid Thursday at a Hyundai manufacturing complex in Ellabell, Georgia, officials said Friday, calling it the largest single-site enforcement operation in the history of Homeland Security Investigations.

Steven Schrank, the special agent in charge of Homeland Security Investigations in Georgia, said the operation resulted from a months-long investigation into allegations of illegal hiring at the sprawling site and that most of those detained were South Korean nationals. Schrank said officials were still determining the precise nationalities and legal status of all who were detained and that no criminal charges had been filed immediately following the operation.

The enforcement action focused on an adjacent plant that remains under construction and where Hyundai Motor Group has partnered with LG Energy Solution to produce batteries for electric vehicles. The broader Hyundai complex, where the automaker began assembling electric vehicles about a year ago with a reported $7.6 billion investment, employs roughly 1,200 people in an area about 25 miles west of Savannah that state officials had hailed as a major economic development project.

Video and images released by witnesses and media outlets showed rows of workers seated on grass outside the facility as federal agents, some wearing masks, monitored the scene. Authorities said the detained workers were suspected of working in the United States without authorization; officials characterized the population of those detained as including people who entered the country illegally and others who had overstayed visas or otherwise lost legal work authorization.

Authorities did not immediately provide a breakdown of how many people would face removal proceedings, be released, or be subject to other administrative actions. Homeland Security Investigations coordinates criminal and civil immigration enforcement, and its operations can result in a range of outcomes depending on individual circumstances and potential employer-related criminal investigations.

The plant and its partners have been prominent in state economic development discussions. Gov. Brian Kemp and other state and local officials previously promoted the facility as one of the state’s largest economic projects in recent years. Company officials have not released a detailed public statement addressing the raid as of Friday afternoon.

The operation drew immediate attention because of its scale and the profile of the site. Schrank described the action as the agency’s largest single-site enforcement operation in roughly two decades of the agency’s existence. Federal immigration enforcement officials said the effort was the culmination of an extended probe into hiring practices at the complex and adjacent construction site.

Rows of workers seated outside the factory watched over by federal agents

Federal officials said processing for the detained individuals would continue as investigators and immigration officers determine legal status and next steps. The Department of Homeland Security did not immediately provide additional operational details Friday, and court records related to the investigation had not been released publicly.

The raid is likely to prompt scrutiny from lawmakers, labor advocates and immigrant communities, and it underscores the ongoing focus on workplace immigration enforcement at large manufacturing sites. Officials said the investigation was ongoing and that they would provide further information as it becomes available.