A copy of the draft annual progress report on Turkey's EU candidacy, seen by Reuters, also cites a severe deterioration in the security situation and an increasing politicisation of the state administration as Erdoğan's AK Party, in power for the last 13 years, tightens its grip.
The EU executive, which is urgently trying to secure Erdoğan's help to stem flows of Syrian refugees and other migrants from Turkey to Europe, insisted it had not delayed the report for political reasons.
It also said it was up to Commission President Jean-Claude Juncker to decide when the progress reports on candidate countries, usually released in October, are approved and published.
In the forensic language of the Commission's department for enlargement negotiations, the draft describes an overall drift towards more authoritarian governance in Turkey.
"The outgoing government has made efforts to reinvigorate the EU accession process," it says. "However, this commitment was offset by the adoption of key legislation in the area of the rule of law, freedom of expression and freedom of assembly that ran against European standards."
It depicts a court system increasingly under the thumb of the government or subject to undue political duress.
"The situation has been backsliding since 2014," it said. "The independence of the judiciary and the separation of powers have been considerably undermined and judges and prosecutors have been under strong political pressure."
The report also hinted at criticism of Erdoğan's personal exercise of power, saying the president remained engaged in a wide range of foreign and domestic policy issues, leading to criticism in Turkey that he was overstepping his constitutional prerogatives.
Asked about the draft on Wednesday, a Commission spokesperson said the EU executive could not comment on the "substance of the report" before it had adopted the document.
"We have to work with Turkey"
However, EU officials and diplomats said Brussels decided to keep the potentially explosive document under wraps until after Turkey's Nov. 1 parliamentary election - the second national vote this year - because the EU was seeking Ankara's cooperation in stemming the flow of Syrian and other refugees to Europe.
"It just makes sense not to release the report while we are trying to enlist their help with the refugee crisis," a senior Commission official said.
In similarly pragmatic vein, Juncker told the European Parliament on Tuesday that, despite human rights concerns, "whether we like it or not, we have to work with Turkey".
A person familiar with the document said the version seen by Reuters had been written before German Chancellor Angela Merkel visited Istanbul for talks with Erdoğan on Oct. 18. It was not clear whether the wording would be toned down when the report is finally published.
Erdoğan has been seeking an absolute parliamentary majority to change the constitution and give executive powers to the presidency that have previously been wielded by the prime minister and the government.However opinion polls suggest an outright majority will again elude his moderately Islamist AK Party on Sunday and that it may have to govern in coalition with one of the secular opposition parties, making it hard for Erdoğan to reshape the state to boost his own power.