US President Donald Trump on Monday set a 25% tax on goods imported from Japan and South Korea, as well as new tariff rates on a dozen other nations that would go into effect on Aug. 1, EDnews reports, citing AP.

Trump provided notice by posting letters on Truth Social that were addressed to the leaders of the various countries. The letters warned them to not retaliate by increasing their own import taxes, or else the Trump administration would further increase tariffs.

“If for any reason you decide to raise your Tariffs, then, whatever the number you choose to raise them by will be added onto the 25% that we charge,” Trump wrote in the letters to Japanese Prime Minister Shigeru Ishiba and South Korean President Lee Jae Myung.

The letters were not the final word from Trump on tariffs, so much as another episode in a global economic drama in which he has placed himself at the center. His moves have raised fears that economic growth would slow to a trickle, if not make the U.S. and other nations more vulnerable to a recession. But Trump is confident that tariffs are necessary to bring back domestic manufacturing and fund the tax cuts he signed into law last Friday.