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.

Trump delayed the "reciprocal tariffs" in April, vowing to strike roughly 90 trade deals in 90 days. So far, the White House says it has reached trade agreements with only the United Kingdom and Vietnam, as well as a preliminary accord with China.

Wall Street is pointing to a lower open Monday as the Trump administration steps up pressure on trading partners to quickly make deals before a Wednesday deadline. The U.S. will warn trading partners that higher tariffs could kick in Aug. 1.