SEOUL, Sept. 9 (Xinhua) -- Hundreds of South Korean workers have been detained following last week's immigration raid in the United States, raising concerns among South Korean companies about investment in the U.S.

The detained workers were expected to return home in a chartered flight later this week, Yonhap news agency said Monday, citing a South Korean diplomat.

WHAT HAPPENED

In collaboration with federal, state and local law enforcement agencies, agents of the U.S. Immigration and Customs Enforcement (ICE) executed a federal search warrant on Sept. 4 at a company due to serious allegations of unlawful employment practices and other potential federal crimes, the ICE said on its website.

The immigration raid occurred at the construction site of an electric vehicle battery plant operated by a joint venture between Hyundai Motor Group and LG Energy Solution.

Arrested were 475 individuals, reportedly including about 300 South Korean nationals who have since been held at the Folkston detention center in Geogia.

The ICE said that the detainees were found to be working illegally in violation of the terms of their visas as people on short-term or recreational visas are not authorized to work in the U.S.

South Korean President Lee Jae-myung ordered diplomats to make all-out efforts to promptly resolve the issue, saying the rights and interests of South Korean people and the economic activities of South Korean companies should not be unfairly infringed upon in the course of law enforcement in the U.S.

Kang Hoon-sik, presidential chief of staff, said Sunday that negotiations had been concluded for the release of the detained South Koreans, noting that once administrative procedures are completed, a chartered plane will depart to bring the South Koreans home.

CONCERNS ABOUT INVESTMENT

The raid came just over one week after U.S. President Donald Trump met with Lee Jae-myung in Washington for their first summit.

South Korea has pledged an investment package of 350 billion U.S. dollars in the American manufacturing sector, but final details of the investment were still under negotiation.

Concerns about investment in the U.S. were raised among South Korean companies, of which one executive said, "(The U.S. says) it is an economic alliance when attracting investment but (the U.S.) treats essential manpower for factory construction like criminals," according to the local newspaper Chosun Ilbo.

Small and medium-sized companies, which started business with large companies in the U.S., would inevitably suffer massive losses and stop business if their business is delayed due to visa problems, the newspaper added.