Germany and France have said that they will respond "firmly" to the US if it imposes tariffs on European steel and aluminum.
On Wednesday, French Economy Minister Bruno Le Maire said that as long-time US allies, the EU does not deserve such actions by the US.
"We will not accept that Europe be struck with tariffs on steel and aluminum. We are allies of the United States. We are friends of the United States and we do not want to be struck with aggressive measures, such as the tariffs," he said while addressing the forum of the Organization for Economic Cooperation and Development (OECD) in Paris.
"So, we will see what our decision will be depending on (US) President Donald Trump's decision, probably by tomorrow during the day," he added.
Meanwhile, German Economy Minister Peter Altmaier said Trump's plan will start a "trade war," to which the EU will respond to with an iron fist.
"Europe is united and firm. We have worked in an extremely intensive manner in recent weeks to avoid the increase in tariffs, to allow for an evolution towards freer markets. But we are also prepared to react," he said.
"We know very well that this is about avoiding a trade war... But to attain this goal, it is extremely important that Europe's message be clear and united," he added.
The comments came amid increasing tensions between the US and the European Union over trade barriers mostly introduced by Washington. The EU insists it should be permanently exempted from tariffs on steel and aluminum, which the US says is mostly aimed at overproduction in China. However, Washington says the EU should give concessions for a current exemption to become permanent.
The EU has proposed that the issue of overcapacity could be resolved through talks if Washington agrees to permanently exempt the EU from the tariffs.
Trump imposed the tariffs in March on the grounds that American producers crucial to military preparedness were being undermined by cheap imports.
The EU countries have warned that they could also impose their own punitive tariffs on US-made goods. Those tariffs would affect 2.8 billion euros' ($3.4 billion) worth of US exports, while the EU’s metal exports to the United States, which could be affected by new tariffs, are worth 6.4 billion euros.