Update: Since this article was published Croatia has been given the green light to join Schengen, while Romania and Bulgaria have been blocked. Click here for the latest.
The enlargement of the passport-free Schengen Area to take in Romania and Bulgaria has been put in serious doubt ahead of an expected vote on Thursday.
Austria and Netherlands continue to have concerns about admitting one or both of the countries.
The opposition has been brewing for days but became patently clear on Wednesday after EU ambassadors met to discuss the topic.
Interior ministers from the European Union are expected to decide on the long-stalled candidacies today. A unanimous endorsement is required to admit new members into Schengen and abolish checks at all internal borders.
"Austria is the main hold-out," an EU diplomat said on Wednesday afternoon, speaking on condition of anonymity due to the sensitivity of the issue.
"It's already clear that there is no unanimity," said another diplomat. "Those who don't agree will make their points of view heard during the debate."
Austria argues the new influx of asylum seekers through the Western Balkan route demonstrates that Schengen is unable to cope with migration management, even if Romania is not part of that route.
The country says it has received 75,000 unregistered migrants this year, a number that poses a "security issue that we cannot wipe away," Austrian Chancellor Karl Nehammer said on Wednesday.
Nehammer called for a five-point plan to strengthen Schengen and asked for the vote on the joint bid to be delayed "until next august."
Austria's position, which for many came as a surprise, has infuriated Romania and Bulgaria, who countered their bids are unconditionally backed by the European Commission, the European Parliament and a vast majority of member states.
"The current state of uncertainty cannot continue. We have all the arguments, very solid, that support our requests," Romania's Prime Minister Nicolae Ciucă said on Wednesday.
"We basically can't talk about a real justification at this point."
For its part, the Netherlands is open to Romania's accession but remains opposed to Bulgaria's entry over what they say are unaddressed rule-of-law elements.
Bulgaria has had a caretaker government since August after a series of inconclusive elections.
However, both Austria and the Netherlands intend to support the third outstanding candidate to join Schengen: Croatia, making its admission a foregone conclusion.
"The few hesitations that remain are political, and they undermine two very simple facts that we are stronger, not weaker, through Schengen enlargement," European Commission Vice-President Margaritis Schinas told reporters ahead of Thursday's meeting.
"And secondly, that enlarging Schengen means more and better controls, not less."
The Czech Republic, which currently holds the EU Council's rotating presidency, intends to organise two separate votes on Thursday: one on Croatia and a second one on Bulgaria and Romania.
Despite the adverse circumstances, the Czechs still plan to move ahead with the votes, Euronews understands, although the agenda could change at the last minute.
Diplomats admit that even if Romania managed to overcome Austria's opposition, it would still be blocked from joining Schengen because its bid has become politically and technically intertwined with Bulgaria's.
"Decoupling is very complicated for legal and technical reasons. The Council would have to ask an opinion from the European Parliament before being able to come back to the issue," an EU diplomat said.
"That would not be really helpful."
A negative outcome on Thursday would deal a political blow to both Romania and Bulgaria, as the duo has been on Schengen's waiting list since at least 2011 – years before Croatia.
The European Commission and the European Parliament have concluded the two countries are ready to join the Schengen Area and urged member states to endorse their bids without any further delay.
Over the last few years, France, Germany, Sweden, Denmark, Finland and Belgium – countries that in the past opposed Schengen enlargement – have softened their position and become agreeable.
But as accession requires unanimity, one simple "no" can scupper the whole agreement.
The Council could revert to the issue in March, under the upcoming Swedish presidency, diplomats said.
Ivan Demerdzhiev, Bulgaria's interim Interior Minister, implied his country would retaliate against Austria and the Netherlands if his country's bid is unsuccessful, but gave no further details on what that would mean in practice.
"The Netherlands and Austria are trying to overcome their internal problems through the position they take on Bulgaria, but it should be clearly noted that this is not the European position. Our response will be reciprocal to what we receive," Demerdzhiev told Euronews Bulgaria on Tuesday.
"When we are asked to take a position on such issues, we will also bear in mind that we do not always have to stick to what exists as the values of the Union, as the principles of action of the Union, but that we could also solve various other problems through our (own) positions, which concern European issues."
Schengen enables cross-border travel without the need to carry a passport or pass through border controls. It currently encompasses 26 countries, including 22 EU member states, and almost 420 million citizens.
Joining Schengen is a legal obligation for every EU country.
Only Ireland, who decades ago negotiated an opt-out clause, and Cyprus, who remains split between north and south, have not applied to join the passport-free area.