US President Donald Trump is likely to dust off a 1930 trade law, largely forgotten for decades, to back his new reciprocal tariffs that will match other countries’ higher import taxes, trade and legal experts say.

U.S. President Donald Trump said he would impose reciprocal tariffs as soon as Wednesday evening on every country that charges duties on U.S. imports, in a move that ratchets up fears of a widening global trade war and threatens to accelerate U.

White House Press Secretary Karoline Leavitt told reporters Wednesday afternoon she believes Trump will unveil his reciprocal tariffs Thursday morning; Trump had told media Sunday he will announce the measures “probably Tuesday or Wednesday.