U.S. President Donald Trump on Monday began telling trade partners – from powerhouse suppliers like Japan and South Korea to minor players – that sharply higher U.S. tariffs will start August 1, marking a new phase in the trade war he launched earlier this year.

President Donald Trump cranked up the pressure on two of America’s key trading partners, Japan and South Korea, firing off letters Monday to the heads of their countries that informed them of their new tariff rate.