Trump sent letters to 14 countries threatening them with new tariffs, and the White House said more countries may be included in the coming days.

President Trump on Monday said the U.S will impose 25% tariffs on goods from South Korea and Japan by Aug. 1, while also threatening to hit a dozen other nations with steep import duties by next month.

President Donald Trump cranked up the pressure Monday on America’s trading partners, firing off letters to heads of several countries, informing them of their new tariff rate. But at the same time, Trump took some of the edge off by signing an executive action Monday to extend the date for all “reciprocal” tariffs,

Stocks fell on Wall Street as the Trump administration stepped up pressure on trading partners to make deals before punishing tariffs imposed by the U.S. take effect. The S&P 500 lost 0.8% Monday.