MEPs adopted on Wednesday a report warning that the relations between Turkey and the European Union were at a "historic low point."
The text was passed with 480 votes in favour, 64 against and 150 abstentions.
Rapporteur Nacho Sánchez Amor said the report was "probably the toughest yet in its criticism of the situation in Turkey".
MEPs said Turkey had distanced itself from European values and continued backsliding in the field of rule of law. They blamed Turkey's President Recep Tayyip Erdogan for his authoritarian moves. The last two years saw an unprecedented crackdown on opposition and on media, according to the report.
Despite spiralling tensions, Turkey has been a candidate country to the EU for more than 15 years. But the European Parliament say accession negotiations should be formally suspended if Turkey does not change course.
"Because the accession process is not driving democratic reforms, the European Parliament is committed to include democratic conditionality in every aspect of our relationship", said Sánchez Amor.
Turkey is a key partner for the EU, with security and migration as the main areas of cooperation. In this context, even if more voices support an immediate suspension of Turkey's candidacy, some MEPs agree on giving Ankara another chance for talks.
"Turkey cannot be a member of the European Union", said EPP leader Manfred Webber. Instead, he demanded "a special way of partnership of good neighbourhood".
Webber emphasised that Turkey and the EU "need each other". This opinion is shared by the Commission and the Council, which are also eager to increase cooperation with Ankara.