SAVANNAH, Ga. — A lawyer for several workers detained at a Hyundai factory in Georgia says many of the South Koreans rounded up in the immigration raid are engineers and equipment installers brought in for the highly specialized work of getting an electric battery plant online.

Atlanta immigration attorney Charles Kuck, who represents four of the detained South Korean nationals, told The Associated Press on Monday that many were doing work that is authorized under the B-1 business visitor visa program. They had planned to be in the U.S. for just a couple of weeks and “never longer than 75 days,” he said.

“The vast majority of the individuals that were detained by U.S. Immigration and Customs Enforcement that were South Korean were either there as engineers or were involved in after-sales service and installation,” Kuck said.

The raid Thursday at the battery factory under construction at Hyundai’s sprawling auto plant west of Savannah resulted in the detainment of 475 workers, more than 300 them South Koreans. Some were shown being shackled with chains around their hands, ankles and waists in video released by U.S. Immigration and Customs Enforcement.

South Korea’s foreign minister was flying to the U.S. on Monday to secure his citizens’ return on a charter flight to South Korea, where many people have expressed confusion, shock and a sense of betrayal.

President Donald Trump said the workers “were here illegally,” and that instead, the U.S. needs to arrange with other countries to have their experts train U.S. citizens to do specialized work such as battery and computer manufacturing.

But immigration lawyer Kuck said no company in the U.S. makes the machines that are used in the Georgia battery plant, so they had to come from abroad to install or repair equipment on-site — work that would take about three to five years to train someone in the U.S. to do, he said.