Chief among these is the requirement for the Turkish government to change its anti-terror laws that have been used to silence journalists, media outlets and critics of President Recep Tayyip Erdogan, which Turkey has flatly refused to do.
In a sign of the tensions, the chief EU ambassador conducting the negotiations, Hansjörg Haber, was reported in the newspaper Hurriyet, as saying:
"We have a proverb, 'To start like a Turk and end like a German,' but it has been just the opposite here [in these negotiations]. It started like a German and is being finished like a Turk."
His comments forced the Turkish EU Minister and Chief Negotiator Volkan Bozkır to say: "The German ambassador of the EU should explain to the Turkish nation what he meant when he said 'like a German and like a Turk.' No diplomat and especially no ambassador can address the president of a country where he is posted for his job like this.
"An ambassador does not have the right to humiliate the country and people where he is located and say a word against the president. This is the first principle of diplomacy," said Bozkır.
Not a Safe Country
The row is the latest in a series of setback over the migrant deal, which would see relocated migrants from Greece being swapped on a one-for-one basis with Syrian refugees from camps in Turkey, who would be relocated to EU member states. However, so far fewer than 200 have actually been relocated from Greece.
Many humanitarian aid NGOs have joined the UN Refugee Agency UNHCR in saying the EU-Turkey deal is either immoral or illegal as the 'hotspots' have become detention centers. They also say Turkey is not a 'safe country' for migrants to be returned to, under the Geneva Convention.
Press release regarding the proposal of the European Commission about visa liberalization for Turkish citizens https://t.co/6jph1KtnqE— Turkish MFA (@MFATurkey) 5 May 2016
EU lawmakers on the Civil Liberties Committee MEPs have repeatedly quizzed the EU Commission about the conditions in the Greek reception centers, the number and background of staff conducting asylum interviews and the return of migrants and asylum seekers to Turkey.
They are especially concerned about the situation of vulnerable groups, such as women with children and unaccompanied minors.