"They were illegal aliens and ICE [Immigration and Customs Enforcement] was just doing its job," President Donald Trump said following the raids on Friday.
Video released by ICE officials showed Asian workers shackled in front of a building, with some wearing yellow vests with names such as "Hyundai" and "LG CNS".
"People on short-term or recreational visas are not authorized to work in the US," ICE said, adding that the raid was necessary to protect American jobs.
"This operation sends a clear message that those who exploit the system and undermine our workforce will be held accountable," Homeland Security Investigations (HSI) Special Agent Steven Schrank said in a statement on Saturday.
South Korea, a close US ally, has pledged tens of billions of dollars in American manufacturing investment, partly to offset tariffs.
The timing of the raid, as the two governments engage in sensitive trade talks, has raised concern in Seoul.
Trump has actively encouraged major investments from other countries while also tightening visa allocations for foreign companies.
Many of the LG employees arrested were on business trips with various visas or under a visa waiver programme, officials say.
South Korea's Minister of Foreign Affairs Cho Hyun said he felt a "great sense of responsibility for the arrest of our citizens" as he presided over an emergency meeting about the issue on Saturday.
He said the government had set up an Overseas Korean Protection Task Force to respond to the arrests and that he may travel to Washington if needed.
"Immediately after this incident became known, the President stressed that U.S. law enforcement actions must not unjustly infringe upon the rights of our nationals or the economic activities of our Korean-invested companies," he said.
