President Donald Trump is threatening to impose higher tariffs on Japanese exports to the United States over what he claims is the country’s unwillingness to buy American-grown rice.

Japan will not sacrifice the agricultural sector as part of its tariff talks with the United States, its top negotiator said on Tuesday, after President Donald Trump complained that the key Asian ally was not buying American rice.

The U.S. is preparing to send Japan a letter outlining a new tariff rate for the nation, President Trump said Monday, despite months of intensive negotiations between the countries aimed at averting higher tariffs.