TOKYO (AP) — In unwelcome news for American farmers, Japan said Friday that it was imposing emergency tariffs of 50 percent on imports of frozen beef, mainly from the U.S.

Finance Minister Taro Aso announced the move Friday, saying he was prepared to explain the decision to the U.S. side.

"The tariff will take effect automatically as the volume of the imported US frozen beef exceeded the quota set by law," Aso said, "So this is what has to be done."

Japan's beef farmers are famed for their luscious marbled Kobe beef and other delicacies, and the government has long used tariffs and other measu...