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.

President Donald Trump on Monday placed a 25% tax on goods imported from Japan and South Korea, citing persistent trade imbalances with the two crucial U.S. allies in Asia.

The president has already threatened an additional 10% tariff on goods from countries aligning themselves with a bloc of nations that includes China and Russia.