The European Union will consider next week whether to temporarily suspend the right of US citizens to visit the 28-country bloc without a visa, as some Europeans have not yet been granted visa-free access to the United States.
Europe is US travellers' main overseas destination, with nearly 12 million undertaking the trip in 2014, according to data from the US National Travel and Tourism Office. Currently, Americans can visit EU countries for up to three months without a visa.
Suspending that right could lead to tensions between the EU and US, just as they are working to finalize a landmark free trade deal.
"Our goal remains full reciprocal visa waiver with our strategic partners, and we are working constructively with them on this," European Commission spokeswoman Mina Andreeva told journalists in Brussels on Tuesday.
But the clock is quickly ticking down to an April 12 deadline on which the EU's executive will be obliged to recommend suspending for one year US nationals' visa-free access if EU citizens still do not get the same treatment on the other side of the Atlantic.
The US has yet to grant visa-free access to travellers from the EU countries Bulgaria, Croatia, Cyprus, Poland and Romania - mainly because their citizens too often have their US visa requests rejected, according to a commission report from November.
The reasons for the visa rejections were not listed.
The commission will discuss how to proceed on Tuesday. If it recommends a suspension of the US visa waiver, this would only enter into force after four months, giving EU member states and the European Parliament time to object if they wish.
Australia, Barbados, Brunei, Canada and Japan were also flagged in the November report as having presented visa reciprocity problems.