Hundreds of people including South Korean workers were arrested in an immigration raid at a Hyundai Motor battery plant under construction in Georgia, weeks after the carmaker pledged $26 billion in U.S. investments.

South Korea protested the action to the U.S. and said it was trying to secure the release of its citizens.

Around 450 people were arrested, said the Atlanta office of the Bureau of Alcohol, Tobacco, Firearms and Explosives in a social-media post. The post described the people as “unlawful aliens.”

The raid and arrests come after months of tense negotiations between the U.S. and South Korea over tariffs and investment. In late July, the two countries agreed that a 15% tariff rate would be imposed on South Korean imports in exchange for South Korea investing $350 billion in the U.S.

The factory is being built by a joint venture between South Korea-based Hyundai Motor and a South Korean battery manufacturer, LG Energy Solution. It is located in the town of Ellabell, near Savannah, Ga., and is part of a $7.6 billion Hyundai complex that the state has described as the largest manufacturing project in Georgia’s history.

The plant, once completed, is set to supply batteries to Hyundai Motor’s nearby electric-vehicle manufacturing plant, which opened last year. Hyundai has pledged to employ 8,500 people there by 2031 as part of a $2 billion incentive package it received from Georgia.