Brussels - The European Union will refer the United States to the World Trade Organization (WTO) this week for "unjustified" import duties imposed on olives from Spain, EU Trade Commissioner Cecilia Malmstrom has announced.

In June, the US Department of Commerce decided to impose punitive tariffs on Spanish olives, arguing that these were being sold in the US at up to 25.5 per cent below value, while Madrid was subsidizing olive producers by up to 27 per cent.

The EU protested the move at the time, calling it a "protectionist measure." The issue comes amid a wider trade dispute between Brussels and Washington.

"The duties imposed by the United States on ripe olives from Spain are unjustified, unwarranted and go against the rules of the World Trade Organization (WTO)," Malmstrom has written on Twitter.

"Tomorrow, we are taking this case to the WTO dispute settlement system, requesting consultations with the US," she added, noting that the European Commission will "continue to vigorously defend the interests of EU producers."

Bilateral consultations are the first stage of the WTO dispute resolution process. If both sides fail to solve the problem between themselves, the matter can be ultimately decided by a judicial panel of the WTO.

EU-US trade relations are tense after US President Donald Trump imposed duties of 25 per cent on steel and 10 per cent on aluminium imports last year. Brussels retaliated with tariffs on a range of US products.

The two sides are engaged in trade talks but have made little progress towards launching negotiations on a limited trade deal.