The European Union triggered the first phase of retaliation against the US over its metal-import tariffs imposed on national-security grounds, making good on more than three months of threats to hit American goods with tit-for-tat levies.
European Union countries retaliatory trade tariffs on a list of USA products, agreed in response to U.S. tariff hikes on steel and aluminium imports from Canada, the EU, and Mexico, will come into force on Friday, the European Commission announced on Wednesday.
"However, the unilateral and unjustified decision of the USA to impose steel and aluminium tariffs on the European Union means that we are left with no other choice".
Canada has announced it will impose retaliatory tariffs on C16.6 billion ($12.5 billion) worth of US exports from July 1.
Ms Malmstrom said: "We did not want to be in this position".
Trump's threats to raise tariffs on imported cars could put $54 billion in annual revenue from European passenger auto exports to the U.S.at risk, according to data from the European statistics office.
In March, Trump chose to hit importers with a tariff of 25 percent on steel and 10 percent on aluminum.
Mexico has already put tariffs on US products that include steel and pork. Mexico put tariffs on American products ranging from steel to pork and bourbon two weeks ago.
President Trump insists his tariffs are needed to protect American workers and has said the European Union treats the United States "very unfairly".
The former reality TV star is fighting a trade war on multiple fronts, with China also promising swift retaliation after the United States threatened to impose levies on a further £151bn ($200bn) of Chinese goods.
Together the trade battles have raised the spectre of a global trade war, spooking financial markets that fear major consequences to the world economy.