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South Korean officials are calling for the return of more than 300 of its citizens who were detained last week during an Immigration and Customs Enforcement raid at an electric vehicle battery factory in Georgia. The Department of Homeland Security said it was the largest single-site investigation in the agency’s history. In total, 475 people were arrested.

Immigration officers arrested the workers on Sept. 4 at an under-construction battery factory, which will be part of a huge industrial manufacturing site near Savannah. The anchor of that complex is a new Hyundai electric and hybrid vehicle plant where cars started rolling off the line last year. 

Investigators described the raid as the culmination of a long-running inquiry.

“This was not an immigration operation where agents went into the premises, rounded up folks and put them on buses,” said Steven Schrank, DHS special agent in charge for the region. He said some of the detainees were in the US illegally, while others had overstayed their visas or were using the wrong visa to work.

“This has been a multi-month criminal investigation where we have developed evidence, conducted interviews, gathered documents, and presented that evidence to the court in order to obtain a judicial search warrant,” he said.

Schrank said the workers were employed by contractors, sub-contractors, sub-sub contractors, and investigators were still untangling who was employed where. In a statement last week, Hyundai said based on its “current understanding,” none of those detained worked directly for the Motor Company.

The South Korean government reacted quickly, expressing “concern and regret” over the arrests. Within a few days, officials had negotiated the release of the South Korean workers and announced the country was chartering a plane to bring the workers back to Korea. As of Wednesday morning, the workers are still in Georgia. 

Many of those detained were engineers and equipment installers, according to an Atlanta immigration attorney representing several of them. They were in the U.S. temporarily to get the factory up and running, then train U.S. workers on it, said attorney Charles Kuck. The equipment at the plant is designed and manufactured in Korea and Japan, he said, so it’s standard practice to bring workers from abroad to install it.

“This is not abnormal to have people from a different country come and help set up a factory,” Kuck said. “It would be abnormal if they weren’t here.”

In 2022, when Georgia Governor Brian Kemp first announced that the Hyundai factory would be coming to the state, it was celebrated as “the largest economic development project in our state’s history.” (Georgia has long pushed to become a center of solar panel, electric vehicle, and battery manufacturing, and even has its own economic development office in Seoul.) Soon afterward, then-President Joe Biden signed the Inflation Reduction Act, which enhanced tax credits for electric vehicles and included added incentives for vehicles made in the U.S. 

Last week’s raid may have thrown a wrench into those efforts. Indeed, the business repercussions could be far-reaching, according to Andrew Yeo of the Brookings Institution. 

According to Yeo, work at the battery plant has stopped. “There isn’t going to be any construction for a while as officials try to sort out what has happened and whether Koreans can continue operations,” he said. Yeo stressed that companies should be employing workers legally, and he said this raid will likely discourage future manufacturing partnerships with foreign companies — partnerships that the U.S. needs for the clean energy sector.

“I do think it’s going to put a pause on how countries think about future investments in the U.S.,” Yeo said. “But of course there are other factors at play that have already created some risks to investing in the U.S.”

Those factors include tariffs and the Trump administration’s reversal of many Biden-era policies and incentives on electric vehicles and renewable energy, which have already raised questions about the future of the factories that opened or expanded in response to the Biden incentives.

There is a “disconnect,” Yeo said, between Trump’s calls for foreign investment and onshoring of manufacturing on the one hand and immigration crackdowns on the other hand. But such issues predate the current administration, he said. During the manufacturing growth under Biden, he said, Korean companies complained that they couldn’t hire skilled workers quickly enough. It’s a problem that U.S. policymakers and foreign companies making EV and clean energy products will need to sort out.

“After all, this is how we create a win-win sort of economic alliance between the U.S. and our allies,” Yeo said.

Marlon Hyde and Emily Wu Pearson of WABE contributed to this report.