The European Commission says it will advise EU leaders that accession talks with Turkey should not begin unless Ankara adopts a new penal code.
The adultery clause triggered heated debate in Turkey
"If this central element of reform, that is the new civil code, is not adopted negotiations cannot start," said a Commission spokesman on Monday.
The Commission is due to present a report on 6 October on whether Turkey has met the criteria set by the EU.
A move to criminalise adultery in the penal code has caused much controversy.
Last week Turkish Prime Minister Recep Tayyip Erdogan hit out at the European Union, telling it not to interfere in his country's internal affairs.
He spoke after the European Commission warned that Turkey's bid to join the EU could be complicated by its delay in passing the penal code.
The bill was withdrawn on Thursday because of the adultery row.
EU Enlargement Commissioner Guenter Verheugen summoned the
Turkish ambassador on Saturday to ask for clarification from his
government on Ankara's position on the code.
But Commission spokesman Jean-Christophe Filori said that as far as he knew Ankara had not yet answered, Reuters news agency reported.
The Turkish bill was intended to bring Ankara's laws closer to those of EU member states and was seen as crucial to its chances of EU entry.
However, the entire package of measures is now subject to review and may not be ready in time for the commission's report on Turkey's progress.
Mr Filori rejected Mr Erdogan's criticism of the EU's position, saying "it is not intereference in Turkish affairs, it is the rule of the game if a country wants to be an EU member".
The clause re-criminalising adultery is part of a package of proposed changes to overhaul Turkey's 78-year-old penal code. The reforms also include:
- Tougher penalties for convicted torturers. Torture in police stations and prisons would be punished with 12 years in jail
- Clauses on genocide, crimes against humanity and people-trafficking - the first time such crimes are mentioned in the Turkish penal code
- Stronger laws against rape and so-called "honour" crimes against women.
Mr Erdogan is due to visit Brussels this week to meet the leaders of the new European Parliament and try to ease fears about Turkey's eventual EU membership.
The BBC's Oana Lungescu in Brussels says the process of EU membership talks is highly intrusive - one senior EU official compared it to "voluntary regime change" by countries willing to undergo painful transformations in order to join the bloc.
The question being asked now is whether Turkey is fully willing to do the same, she says.
Mr Filori admitted that "many people say this is not a European country, it's a remote country... it cannot meet our standards".
"So far, in the past two years, Turkey has managed to demonstrate that on the contrary this huge country with Muslim traditions is perfectly able to align on the values of human rights and democracy of the EU.
"But in these last days I have to say that it plays into the hands of all those who are sceptical about Turkey's ability to join the European Union," he said.