Authorities in Turkey decided to re-run the municipal elections in Istanbul, which took place at the end of March, which faced widespread criticism by the opposition.
But Akram Imam Oglu, who declared his victory as a mayor of Istanbul last April, called the re-elections decision as a "betray."
For his part, the European Parliament said that "the decision to have re-elections of the municipality in Istanbul destroys the credibility of democratic elections in Turkey."
Protests were also held in the city, following the announcement of the re-elections on 23 June.
For its part, the US Washington Post newspaper reported that the re-elections of Istanbul would immediately provoke criticism that Erdogan and his party were ready to undermine confidence in Turkish democracy to serve their narrow goals and to maintain control of the largest city in Turkey, along with the financial networks and nepotism reported by the Justice and Development Party over the decades.
The newspaper indicated that Imam Oglu and other successful rivals all over the country have benefited from voters' discontent with Turkey's faltering economy, as well as a rare show of unity by the traditionally divided political opposition.
Jonul Toll, the director of the Center for Turkish Studies at the Middle East Institute in Washington, says that Erdogan's efforts to re-run elections in Istanbul may increase people isolation, especially the young middle-class voters who are already frustrated by his leadership style, and added, "If he wins, it will not be a real victory."
Unorsal Adegozel, the vice president of the Republican Peoples' Party, said the resolution showed that "it is illegal for anyone to win the AKP."
Adegozel wrote on his account on the Twitter social networking site, describing the decision as "a clear dictatorship."
"A regime that rejects the will of the people and does not respect the law cannot be democratic or legitimate," he said.
In a speech published via social media, Imam Oglu condemned the elections commission's decision, saying it was under the influence of the ruling party.
"We will not accept compromises on our principles. This country has 82 million patriots who will fight till the last breath for democracy," he said.
"We have to stand together and be calm, we will win, and we will triumph again," he said.