after Washington imposed tariffs on EU steel and aluminium at the start of June.

The European Commission on Wednesday formally adopted a law putting in place the duties on 2.8 billion euros ($A4.3 billion) worth of US goods, including bourbon, motorbikes and various steel products.

"We did not want to be in this position. However, the unilateral and unjustified decision of the United States to impose steel and aluminium tariffs on the EU means that we are left with no other choice," EU Trade Commissioner Cecilia Malmstrom said.

"The rules of international trade, which we have developed over the years hand in hand with our American partners, cannot be violated without a reaction from our side," she added.

Malmstrom said the EU response was "measured, proportionate and fully in line with WTO rules."

Since the start of June, the EU has been hit by tariffs of 25 per cent on steel and 10 per cent on aluminium imports imposed by US President Donald Trump, who has justified the move on the grounds of national security.

Other countries hit by the US tariffs have also retaliated, raising fears of a global trade war.