Some U.S. steel and aluminium tariffs went into effect in April and additional tariffs begin in July.
Katainen said he did not expect negotiations on updating trade rules to be easy but that they were necessary to save the environment for multilateral trade.
Also Monday, Wisconsin's Harley-Davidson tumbled more than 6% after saying it would move some production out of the USA amid retaliatory tariffs the company said would bring about a "tremendous cost increase".
Last week, the White House introduced a 25 percent tariff on $50 billion of Chinese imports to the country.
The tweet was an apparent reference to a WSJ warning that "President Donald Trump, already embroiled in a trade battle with China, plans to ratchet commercial tensions higher [with investment restrictions]", and Bloomberg's lamentation that the Treasury Department is "putting Washington's trade war with Beijing on a potentially irreversible course". "China and the European Union firmly oppose trade unilateralism and protectionism and think these actions may bring recession and turbulence to the global economy".
Both China and the European Union are coming under pressure from Trump, as the U.S. president seeks to remake a global trading system that he sees as rigged against the world's largest economy.
China and the European Union (EU) vowed to oppose trade protectionism in an apparent rebuke to the United States, saying unilateral actions risked pushing the world into a recession.
Safety driver involved in fatal self-driving Uber crash was watching Hulu
National Transportation Safety Board investigators examining the Volvo that was involved in the crash. The vehicle was in autonomous mode at the time of the collision.
"We have to reform WTO in order to make multilateralism better functioning in the future. If you are in favor of multilateralism, then you have to engage seriously, for instance in reforming the WTO".
As well, US motorcycle maker Harley-Davidson said on Monday that it would move some production overseas to avoid European tariffs, potentially affecting U.S.jobs.
"It is not in the interests of the United States to just be playing defense and creating a fortress America while the EU, China, and others play offense and attempt to set the rules of the game for the next century", he told the AP.
The EU wants other governments to join the group, the Associated Press reported Katainen as saying.
China and the USA are engaged in a trade conflict over tariffs.
A survey released last week by the European Union Chamber of Commerce in China showed that a slim majority of members thought foreign-invested companies are treated unfairly, and nearly two-thirds see a lack of reciprocity between the access to China's markets that they get, and the access Chinese companies get to Europe.
"All we're doing here with the president's trade policy is trying to defend our technology when it may be threatened", Navarro said.
China had also committed to buying 184 single-aisle A320 Airbus planes during Macron's January visit, but the deal has not been finalised.