South Korea said on Monday that it wants hundreds of its citizens, who were arrested last week during a large US immigration raid at a car battery project and are due to be flown home soon, to be allowed to re-enter the United States.

Foreign Minister Cho Hyun is flying out to Washington on Monday evening and will meet with US Secretary of State Marco Rubio during his trip to resolve the issue. Cho also said he would be asking for the US visa system for Korean workers to be streamlined in the future.

About 300 South Koreans were among 475 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.

The raid sent shockwaves through South Korea, a major US ally, which has been trying to finalise a US trade deal agreed in late July. It came just 10 days after South Korea’s new president, Lee Jae Myung, met with US President Donald Trump in Washington and the two pledged closer business ties.

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

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.

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

South Korea Finance Minister Koo Yun-cheol said on Monday that 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 US 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.

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 US, 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 US and will be recalling South Korea-based employees now in the country.

The battery maker said last week it is cooperating with US 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 electric vehicles at the sprawling site was not affected.

The companies declined further comment on Monday.