President Donald Trump is reinstating tariffs on steel and aluminum from Argentina and Brazil, nations he criticized for cheapening their currencies to the detriment of U.S. farmers, and again called on the Federal Reserve to loosen monetary policy.

Linking his trade agenda with his Fed criticism in an early morning tweet, he said the two South American countries “have been presiding over a massive devaluation of their currencies. which is not good for our farmers.”

The president’s action amount to retaliation against two nations that have become alternative suppliers of soybeans and other agricultural products to China, grabbing market share away from the U.S. Argentina’s peso plunged earlier this year on election results putting a left-wing candidate in the presidency. Brazil has intervened multiple times in the past month to support its devaluing real.

Brazil’s President Jair Bolsonaro said he would talk to his economy minister before reacting to Trump’s comments on the Brazilian real and the imposition of steel tariffs.

“If needed, I can also talk to Trump, I have an open channel with him,” he added as he left the presidential palace.

In a second Twitter post, Trump signaled that he wants the U.S. central bank to do something about suppressed currencies.

Trump has long grumbled about the dollar’s strength and urged the Fed to abandon decades of precedent and act to weaken the greenback. The U.S. government’s dollar policy has traditionally been directed by the Treasury Department. That has prompted fears that the U.S. could lead the world into an era of weaponized monetary policy.

While such a currency war hasn’t happened yet, Monday’s move marks the first time Trump has linked the imposition of tariffs explicitly to currency movements. As such, it signifies a potential new phase in his trade wars in which foreign-exchange markets are the battleground.