The hastily arranged talks on Sunday evening - on the eve of the scheduled negotiations with Ankara on Monday - will focus on Austrian demands that the EU considers something less than full membership for the vast, mainly Muslim country.
There is growing speculation that a resolution of the dispute may depend on parallel EU ruminations on Croatia, whose planned start of EU talks has been delayed due to a dispute over an alleged war criminal.
The EU's British presidency has voiced confidence that the Turkey standoff can be resolved before Monday, but diplomats warned that the issue was "on a knife-edge", while Turkey threatened to boycott the talks if it is not satisfied by what is on offer.
"It has been painful, fighting over every word," said one EU source close to the talks, which focus on the exact wording of what the EU is offering Turkey.
EU leaders agreed at a summit in December to start membership talks with Turkey, which has been knocking on the European grouping's door for more than four decades, on 3 October.
But tensions flared again in July when Ankara, while signing an updated customs accord with the enlarged EU, including Cyprus, issued a declaration reiterating its refusal to recognise the Nicosia government.
EU leaders are on Monday to start
membership talks with Turkey
A dispute over how to respond to that was resolved last week, but a row remains over the negotiating framework - the guiding procedures and principles for the accession talks.
It is unclear what change of wording will satisfy Austria. The current draft, accepted by all 24 other EU states, says EU entry is the main aim of the talks.
Vienna would like that replaced, or at least complemented by, an offer of a lesser "privileged partnership".
Turkish leaders, whose reputation for negotiating brinkmanship is well known, have warned they may not turn up in Luxembourg on Monday.
"If we fail to see the honesty we expect, Turkey's response will undoubtedly be very different from what has been said so far," Prime Minister Recep Tayyip Erdogan warned on Friday.
"If we fail to see the honesty we expect, Turkey's response will undoubtedly be very different from what has been said so far"
Recep Tayyip Erdogan,
Turkish prime minister
However, on Saturday, he said he had held a "very positive" phone conversation with Austrian Chancellor Wolfgang Schuessel.
One unknown factor in all this is how much stock Austria puts in neighbouring Croatia being given the green light on Monday to start its talks.
Croatia was originally to have started EU entry talks in March, but its case has been held up by its lack of cooperation with the UN war crimes tribunal, notably over a key war crimes suspect, fugitive General Ante Gotovina.
The court's chief prosecutor, Carla Del Ponte, gave few signs on Friday that things had improved recently during a visit to Zagreb.
While no official link exists between the candidacies of Croatia and Turkey, an EU diplomat noted: "The general feeling is that movement on Croatia would allow it (Austria) to be more flexible on the negotiating framework."
Valery Giscard d'Estaing believes
Turkey has no place in the EU
Schuessel has denied that his position on Turkey was designed to improve his conservative party's chances in a regional election in Styria on Sunday.
On the eve of the talks, former French president Valery Giscard d'Estaing - architect of the EU's near-dead draft constitution - reiterated his opposition to Turkish accession and said most French people agreed, as did most Europeans, according to polls.
"We often complain that our countries are governed without heeding public opinion, and here is the proof," he told a French newspaper.
"The question is whether Turkey is or is not a European country. History and geography say no."