In a surprise move today, President Donald Trump said he would impose tariffs on steel from Brazil and Argentina on the grounds that the devaluation of their currencies has hurt U.S. farmers and manufacturers.

In two tweets today, Trump said Brazil and Argentina have been presiding “over a massive devaluation of their currencies, which is not good for our farmers.”

“Therefore, effective immediately, I will restore the Tariffs on all Steel & Aluminum that is shipped into the U.S. from those countries. The Federal… Reserve should likewise act so that countries, of which there are many, no longer take advantage of our strong dollar by further devaluing their currencies. This makes it very hard for our manufactures & farmers to fairly export their goods. Lower Rates & Loosen — Fed”

The Washington Post noted that the increased tariffs would cause problems for Brazilian President Jair Bolsonaro, who considers himself a Trump ally, and for incoming Argentine President Alberto Fernández, a leftist politician who will take office within a week.