The European Commission is set to recommend granting visa-free travel for Turkish citizens inside Europe’s passport-free Schengen area, despite unease among some EU lawmakers.
The change could take effect from July, but first it requires approval by the European Parliament and member states.
EU officials insist that Turkey has yet to meet some key EU criteria.
The deal was offered in return for Turkey taking back migrants who crossed the Aegean Sea to Greece.
The EU fears that without this deal, Turkey will not control migration.
Turkey has already played its part, and the number of arrivals has fallen significantly, the BBC’s Chris Morris in Brussels reports.
But Turkish officials have made it clear that if the EU doesn’t fulfil its side of the bargain, there is little incentive for Turkey to continue to help, our correspondent adds.
The European Commission is expected to formally recommend visa-free travel after meeting on Wednesday.
The waiver would scrap the requirement for Turks to get a three-month, short-stay Schengen visa for tourism or business trips. But it will not grant Turks the right to get a job in Europe.
The UK, Ireland and Cyprus are not in Schengen – so they will keep the visa requirement for Turkish citizens.
The visa liberalisation deal remains controversial in a number of capitals across the EU – but the Commission says Turkey has made significant progress.
There are several outstanding issues, including Turkey’s legal commitments to protect fundamental rights, our correspondent says.
He adds that tough questions will be asked when this issue is put before the European Parliament and a summit of EU leaders in June.
Turkey has threatened to stop taking back migrants from Greece if the EU fails to deliver on visa liberalisation.
The large influx of migrants and refugees arriving in Europe from Turkey, and from North Africa, has caused a political crisis among EU states.
Under the EU-Turkey agreement, migrants who have arrived illegally in Greece since 20 March are to be sent back to Turkey if they do not apply for asylum or if their claim is rejected.
For each Syrian migrant returned to Turkey, the EU is to take in another Syrian who has made a legitimate request.
2.75m Syrian refugees registered with UN
151 out of 180 countries on World Press Freedom Index
What are the arguments for and against?
Concerns have been raised in the European Parliament that this looks like a reward for Turkey, because of its co-operation in the migrant crisis. Ankara falls short of many EU human rights benchmarks.
MEPs accept that Turkey is a “key strategic partner” for the EU. But they say reforms have slowed down in Turkey in many areas, including freedom of speech and judicial independence.
MEPs voiced concern about continuing fighting in south-eastern Turkey between government troops and Kurdistan Workers’ Party (PKK) rebels, whom the government in Ankara describes as “terrorists”.
The European Commission’s 2015 report on Turkey also complained of politicisation of the Turkish judiciary, widespread corruption, inadequate protection of minority rights and “significant backsliding” on freedom of speech and assembly.
Total number of migrants who crossed the Mediterranean
fewer than April 2015
9,116 Migrants arrived in Italy by sea in April 2016 – down from 16,063 in the same month last year
3,209 Migrants arrived in Greece by sea in April 2016 – down from 13,556 in April 2015
On the plus side, however, the Commission says Turkey has improved conditions for the many Syrian refugees it is hosting – some 2.75 million. It praises Turkey for providing Syrians with access to jobs and schooling for their children.
It also says Turkey is tightening up its admission rules for migrants from countries which “are sources of significant onward migration” to the EU. Afghanistan, Iran and Pakistan are among those countries.
Many nationalities can already visit Europe’s Schengen zone visa-free, including nationals from Latin America and the Caribbean, Hong Kong and South Korea.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.