The EU has proposed tariffs on $20bn (£15bn) of US goods in a long-running dispute over Boeing aircraft subsidies.
The proposal comes after the WTO said earlier this month that the US had failed to remove some Boeing subsidies.
The EU move comes after the US said it was considering tariffs on about $11bn (£8.4bn) worth of EU goods in response to Airbus subsidies.
And it comes after the EU approved plans in April for trade talks with the US designed to reduce trade barriers.
EU Trade Commissioner Cecilia Malmström said: “European companies must be able to compete on fair and equal terms.
“The recent WTO ruling on US subsidies for Boeing is important in this respect. We must continue to defend a level-playing field for our industry.”
The proposed tariffs cover a range of products from aircraft to chemicals and food products including frozen fish, citrus fruit, and ketchup.
The US and the EU have been battling for almost 15 years at the World Trade Organization over subsidies given to US planemaker Boeing and its European rival Airbus.
After partial victories for both sides, each is asking a WTO arbitrator to determine the level of countermeasures they can impose on the other.
The Trump administration last week proposed targeting a seven-page list of EU products for tariffs, ranging from large aircraft to dairy products and wine, to counteract the harm from EU subsidies for Airbus that are worth an estimated $11bn.
The EU has responded with its own list of US imports, including agricultural produce and dried fruit, to planes, tobacco, handbags, suitcases, tractors, helicopters and video game consoles.