"As for deciding on an appropriate EU response ... we expect the [European] commission to come forward with recommendations during the first week of December," said the current holder of the EU presidency on Monday.
Turkey's accession talks are expected to take at least a decade and no guarantees have been given that it will even be able to join at the end of it all.
A Cypriot diplomat held out little hope of Turkey abiding by its commitment to open up its ports.
"I don't think there is anyone who still hopes that Turkey will fulfil its obligations before the end of the year," he said.
He said that the EU presidency deadline was required in order to "prepare as thoroughly as possibly the response of the EU in view of what is a very apparent non-fulfilment of obligations".
For this, he said a "Plan B" is required.
Vanhanen said he wanted the commission, the EU's executive arm, to quickly make a recommendation on Turkey's compliance with the customs agreement so the bloc's foreign ministers can weigh their response at a meeting on December 11.
"I want to make one thing very clear. The presidency has no intention of raising the Turkey issue at the December European Council (the EU summit on December 14-15)," he said, indicating that decisions will be made before that.
EU Enlargement Commissioner Olli Rehn stressed that the Turkey-Cyprus issue should not be allowed to dominate the mid-December EU summit.
He said that a European Commission meeting on December 6, would be "a logical moment to make a recommendation on the Commission's part if Turkey has not fulfilled its obligations".
In a report released early this month, the commission warned Ankara to make progress on the Cyprus problem before the summit or face unspecified consequences, but it stopped short of suspending membership talks immediately.