FILE PHOTO: South Korea's Foreign Minister Cho Hyun attends a meeting with Japan's Foreign Minister Takeshi Iwaya (not pictured) at Foreign Ministry in Tokyo, Japan July 29, 2025. REUTERS/Issei Kato/Pool/File photo

By Joyce Lee and Hyunjoo Jin

SEOUL (Reuters) - South Korea said on Monday it was in talks with the United States over allowing the re-entry of hundreds of its citizens who were arrested last week during a U.S. immigration raid at a car battery project and are due to be flown home soon.

About 300 South Koreans were among 475 people arrested on Thursday at the site of a $4.3 billion project by Hyundai Motor and LG Energy Solution to build batteries for electric cars.

It was the largest single-site enforcement operation in the history of the Department of Homeland Security's investigative operations, and sent shockwaves through South Korea, a U.S. ally which has been trying to finalise a trade deal agreed in July.

The raid came 10 days after South Korea's new president, Lee Jae Myung, met U.S. President Donald Trump in Washington and the two pledged closer business ties.

Addressing reporters before leaving for the U.S. on Monday, South Korean Foreign Minister Cho Hyun called the detention of the South Koreans "a grave situation" and said he would work with Washington on measures to prevent similar incidents.

Seoul said on Sunday that discussions to arrange the release of workers, who were mostly employed by subcontractors, were largely concluded. A plan is in the works to fly them home on a chartered plane this week under what one South Korean foreign ministry official said would be called a "voluntary departure".

"From the beginning, we negotiated with the premise that there should be no personal disadvantage (to the detained workers)," Cho told a parliamentary hearing on Monday.

U.S. Department of Homeland Security Secretary Kristi Noem said many of the people detained in the Georgia operation would be deported.

"People that are in this country illegally need to know right now, today, that they have an opportunity to go home before they are detained," Noem told reporters on the sidelines of a ministerial meeting in London.

Details on how the workers may have breached immigration rules have not been released by authorities or the companies, but South Korean lawmakers said on Monday some may have overstepped the boundaries of a 90-day visa waiver programme or a B-1 temporary business visa.

Finance Minister Koo Yun-cheol said he had heard that some experts had travelled from South Korea to help with a test run of the factory, which was due to begin production in October.

"You need to get a visa to do a test run, but it's very difficult to get an official visa. Time was running out, and I think experts went to the United States," he said.

DISMAY IN SOUTH KOREA

Seoul has expressed its unhappiness about the arrests and the public release of footage showing the operation, which involved armoured vehicles and the shackling of workers.

Trump, who has ramped up deportations nationwide as his administration cracks down on illegal immigrants, said last week he had not been aware of the raid. He called those detained "illegal aliens".

On Sunday, he called on foreign companies investing in the U.S. to "respect our Nation's immigration laws", but sounded more conciliatory.

"Your Investments are welcome, and we encourage you to LEGALLY bring your very smart people, with great technical talent, to build World Class products, and we will make it quickly and legally possible for you to do so," he said on Truth Social.

In addition to potentially fraying bilateral ties, the development has shone fresh light on how many foreign firms investing in the U.S. have struggled to find qualified American workers.

Hyundai Motor is one of the biggest foreign investors in the United States and is among South Korean companies participating in a pledge of $150 billion in foreign direct investment in the U.S., which comes on top of a $350 billion fund that the South Korean government has separately pledged.

A spokesperson for the automaker said some staff had been asked to suspend non-essential trips to the United States.

LGES has also suspended most staff business trips to the U.S. and will be recalling South Korea-based employees now in the country.

The battery maker said last week it is cooperating with U.S. authorities and had paused construction work on the factory.

A Hyundai Motor spokesperson said last week none of the people detained were employed directly by the automaker and that production of EVs at the sprawling site was not affected.

The companies declined further comment on Monday.

(Reporting by Hyunjoo Jin and Joyce Lee; Additional reporting by Ju-min Park, Heejin Kim, Yena Park and Heekyong Yang in Seoul, Alistair Smout in London; Writing by Jack Kim and Ed Davies; Editing by Edwina Gibbs and Helen Popper)