Last year, Turkey agreed to extend a customs union deal with the EU to include Cyprus, a full member of the EU since 2004.
The deal is considered a tricky bit of diplomacy as Turkey negotiates with the EU's 25 member states but does not recognise the Republic of Cyprus. Ankara has not ratified the deal, and its ports and airports are not open to Greek Cypriot aeroplanes or shipping.
Olli Rehn, the European commissioner for enlargement, has threatened an EU-Turkey "train crash" if Turkey's ports stay closed. But the Turkish response has been tough.
From Recep Tayyip Erdogan, the prime minister, down to junior ministers, Turkey has insisted that it will not open its ports, until the EU fulfils its promises [made in 2004] to end the economic isolation of northern Cyprus, and allow the Turkish Cypriots to trade directly with the EU.
The EU says that the two issues are not related.
Mehmet Dulger, a leading member of parliament from the ruling AK party and chairman of the foreign affairs committee of the Turkish parliament, says the Cyprus problem should not be allowed to derail Turkey's EU talks.
"Let's say we open all our ports; the Greek Cypriots will then ask for other things and other things. It was a huge error of the EU accepting a country with such a conflict," he told Aljazeera.net.
"If requirements of one side of the conflict become the requirements of the EU, it is very difficult to explain to the Turkish public. So it's not acceptable this pressure to Turkey and the government – any party would do it [refuse to open ports] because we are put in the position of preferring half an island to 70 million people."
Talat personifies the island's
pro-EU Turkish Cypriot forces
Turkish public opinion towards the EU has been getting less positive in the face of the EU's demands on Cyprus, and is not helped either by leading European politicians opposing Turkey's membership bid.
Kemal Kirisci, professor at Istanbul's Bosphorus university, is dismayed: "In the last 12 months, the denigrating discourse of [French interior minister Nicolas] Sarkozy and [Austrian Chancellor Wolfgang] Schuessel and others has led to declining public support levels for the EU, and this is aggravated by internal political dynamics."
Nationalism v Europeanism
The decline in the EU's popularity is likely to play a role in next year's presidential and parliamentary elections, with opposition parties playing both nationalist and Eurosceptic cards.
Political dynamics in the EU are not likely to help either. The union is still unsure how to deal with its stymied constitutional project, rejected over a year ago by French and Dutch voters.
As one former EU diplomat told Aljazeera.net: "The EU is in a deep crisis – it's an institution without a compass."
While the EU dithers over its own political direction, a general anti-enlargement mood is growing.
A package of political reforms
has eluded consensus in Cyprus
And even those in the EU who want to prevent a Turkey-EU train crash this autumn, are dismayed at the slowdown they see in Turkey's political reforms.
In late September, Turkey's politicians debated a ninth package of political reforms in the hope of improving the mood when the European Commission issues its annual report on Turkey's progress in negotiations, due in early November.
Without reforms, particularly in the vein of freedom of speech, the increasingly sour atmosphere between Ankara and Brussels looks set to continue unless there is some breakthrough on the Cyprus ports issue.
Nevertheless, the Finns - currently holding the EU's six-month rotating presidency - are still making intense behind-the-scenes efforts to push the Greek and Turkish Cypriots to a compromise deal around the opening up of Famagusta port in the north of the island, and on pushing forwards new UN talks on a comprehensive settlement.
This, Finnish diplomats hope, could then smooth the way to Turkey opening its ports to Greek Cypriot vessels.
But although the two Cypriot leaders - Tassos Papadopoulos and Mehmet Ali Talat - met in July under UN auspices for the first time in two years, attempts to start new so-called technical talks between the two sides are at a stalemate on procedural issues.
At a press conference on the margins of the UN General Assembly last month, Greek Cypriot president Papadopoulos said: "We have not been idle, but I am very sad to say not much progress has been made until now."
And in August, leading Turkish Cypriot adviser to Talat, Rashit Pertev, was pessimistic on a deal linking the opening of Famagusta to handing the nearby closed town of Varosha back to the Greek Cypriots.
"The whole island is one big anomaly," he said.
"[A deal on Famagusta] is wishful thinking. The EU should look at the whole problem, at the root of the problem, instead of trying to come up with cosmetic solutions that may save the day. We 200,000 Turkish Cypriots are Europeans that have been disenfranchised. We have no voice in EU decision-making mechanisms, no access to anything."
The Finns have not yet given up on a Cyprus deal, however, and the European Commission's report, due on October 24, was recently put back two weeks to November 8 to give them more time to push for a compromise.
Against the odds
If they succeed in pushing the two sides in Cyprus to a deal on allowing direct trade for the north of the island, then Turkey will have no reason left not to open up its ports.
The outcome matters not only to Turkey. As economics minister, and chief negotiator with the EU, Ali Babacan put it to a Turkey-EU conference in Istanbul two weeks ago: "The Turkey accession process is important for Turkey and for the EU and for a much wider geography. The change process in Turkey is being monitored in countries in North Africa, the Middle East, the Caucuses and Central Asia."
But if the pessimists are right, and the clash over Cyprus is unresolved, then the EU will find itself mired in an internal debate in November over how to penalise Turkey for not opening its ports to Greek Cypriot shipping.
Many in Turkey are, perhaps rather overconfidently, expecting the EU to suspend negotiations just on three or four chapters (of 35 negotiating chapters) directly related to the customs union
Mehmet Dulger says he is an optimist on the issue: "You can argue and have difficult moments even in a family. I'm an optimist because from the beginning we had the possibility of [EU member states] vetoing the talks and they didn't."
But others are worried that in the face of a stiff EU penalty and tough pre-electoral dynamics in Turkey, Turkey could just walk away from the negotiations.
In this worst-case scenario, the knock-on political impact will be serious but unpredictable.
"Turkey moving towards the EU brings an important political stability to the region – for Turkey, Greece, Turkish Cypriots and Greek Cypriots.
If we go into a situation where Turkey is excluded from the EU, that dream of a peaceful region within the overall EU umbrella gets shattered and we can't predict what will happen after that," Pertev, the adviser to Talat, said.