The 25 percent tariffs that U.S. President Donald Trump decided to impose on automobiles and key auto parts produced outside of the United States officially went into effect Wednesday.

Automobile parts subject to the tariffs include engines, transmissions, powertrains and electrical components.

The Trump-led tariffs are expected to be a significant blow to South Korea, as automobiles are the country’s No. 1 export item to the U.S.

Last year South Korea’s automobile exports to the U.S. amounted to over 34-point-74 billion U.S. dollars and accounted for nearly half the country’s global auto exports.