Tata Steel has urged the EU to take “swift and robust action” in response to a US decision to impose a 25% tariff on European steel.
The US said the tariffs on imports from the EU, Mexico and Canada will start at midnight.
The tariffs will impact directly on Port Talbot as around 10% of Tata Steel Europe’s exports go to the US.
Liberty Steel’s Welsh plants including Newport will not be affected, but it could hit parts of its UK operations.
Almost 7,000 workers are employed by Tata in Wales, including about 4,000 in Port Talbot – the largest steelworks in the UK.
The Community union called on trade unions across the world to stand together to oppose the measures.
The US announcement of tariffs on steel and aluminium immediately triggered vows of retaliation from Mexico and the EU, which called the tariffs “protectionism, pure and simple”.
Henrik Adam, chief commercial officer of Tata Steel in Europe, expressed disappointment at the decision.
“We have been, and will continue, to work closely with our customers on potential product exclusions as the vast majority of the products Tata Steel Europe exports to the US cannot be made by US steel companies, such as our extra wide strip, battery quality hot rolled material as well as certain packaging steels,” he said.
He urged the UK and Netherlands governments, the EU and European trade bodies to continue talks with the US to find a solution.
“We now call on the EU Commission to take swift and robust action to combat the indirect effects of these tariffs,” he said.
“We must ensure our markets are not destabilised by millions of tonnes of steel being diverted away from the US and into Europe. The European Commission now needs to put in place protection measures on a provisional basis without delay.”
Roy Rickhuss, General Secretary of Community, the steelworkers’ union, said steelworkers on both sides of the Atlantic had been let down by their governments.
“Trade unions across the world must stand together in opposition to these measures,” he said.
The problems of steel dumping will not be solved by unfair tariffs, and steelworkers in the UK and USA must not fall into the trap of believing rhetoric from the likes of Donald Trump.
“The UK Government must support EU safeguards to protect our industry and ensure more dumped steel does not end up on European shores.”
Tony Brady, Unite national officer, described the measures as blunt and short-sighted.
Labour MP for Aberavon, Stephen Kinnock, said the decision was a “major setback for the British steel industry”.
The Bush administration introduced steel tariffs in 2002 which lasted for 20 months.
It prompted threats of retaliation from the European Union on US products before the policy was abandoned.