U.S. President Donald Trump says he will only lower tariffs for countries that open their markets, while those that refuse could face much higher tariffs.

Trump issued the warning on Wednesday in a post on his social media platform Truth Social, saying Japan’s markets are now open to the U.S. for the first time. 

In a separate post, Trump said he will always give up tariff points if he can get major countries to open their markets to the U.S., pointing to the “great power” of tariffs and adding that without them, it would be impossible to get countries to open up. 

Trump posted the messages after he announced trade deals with Japan, the Philippines and Indonesia on Wednesday ahead of the August 1 deadline for tariff talks. 

Trump appears to be increasing pressure on countries that have yet to finalize trade agreements with the U.S. 

South Korea sent top trade and industry officials to Washington this week, including Trade Minister Yeo Han-koo and Industry Minister Kim Jung-kwan, in a bid to negotiate a deal.