If the US moves forward with its tariffs, the European Union has threatened to impose retaliatory tariffs on USA orange juice, peanut butter and other goods in return.
European Union Ambassador to the United States David O'Sullivan said earlier that the EU will likely respond with "counterbalancing" tariffs on U.S. products.
Commerce Secretary Wilbur Ross told French daily Le Figaro it would be announced either before markets opened or after they closed.
U.S. President Donald Trump is placing steel and aluminum tariffs on Canada, effective midnight tonight.
European and United States equities lost ground slightly on fears the U.S. measures could spark a trade war.
The two sources briefed on the matter said the decision would land before a Friday expiration deadline for exemptions to the planned tariffs.
On Thursday, the Trump administration is expected to announce that the United States will impose steel and aluminum tariffs on European Union states.
"Realistically, I do not think we can hope" to avoid either USA tariffs or quotas on steel and aluminum, said Cecilia Malmstrom, the European Union's trade commissioner.
US President Donald Trump announced in March that he would slap a 25% tariff on imported steel and a 10% tariff on imported aluminium, citing national security interests.
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The storm surrounding family separations by immigration authorities has been brewing for several months. He has incorrectly blamed the Democrats for the practice, saying: "We have to break up families".
"We look forward to continued negotiations with Canada and Mexico on one hand and with the European Commission on the other hand as there are other issues we need to get resolved", Ross told reporters on a conference call.
But he said that US officials are "quite willing and eager" to have further discussions with all of the parties.
"We continue to be quite willing and indeed eager to have further discussions", Ross said.
French Finance Minister Bruno Le Maire called the USA tariffs "unjustified, unjustifiable and risky".
"By people representing us who didn't have a clue". "We are ready to rebuild this multilateralism with our American friends", he said.
'But they can also increase costs more broadly for USA manufacturers who cannot source all their needs locally and have to import the materials.
The latest federal attempt to ward off the tariffs coincided with a concerted effort by Canada and its European allies to try to stop the Trump administration from imposing the tariffs this week.
"Unilateral responses and threats over trade war will solve nothing of the serious imbalances in world trade". NAFTA negotiations are deadlocked over tough protectionist demands from the United States.