Bülent Tezcan, deputy chairman of the main opposition Republican People’s Party (CHP) is being investigated after he called President Recep Tayyip Erdoğan a “fascist dictator,” Turkish media reported.

The Ankara Chief Prosecutor’s Office on Tuesday launched the investigation after Hüseyin Aydın, a lawyer for Erdoğan, filed a criminal complaint against the CHP’s Tezcan for the “crime of insulting the president.”

According to the Turkish Penal Code (TCK), insulting the president is punishable by up to four years in prison.

“I do not know if [Süleymanpaşa district] Mayor Ekrem [Eşkinat] said that or not. But I am saying this in Tekirdağ Square: Recep Tayyip Erdoğan is a fascist dictator. I am saying this in a way that they understand. [He] is a genuine dictator, in fact,” said Tezcan during a speech in Tekirdağ.

Tezcan visited Tekirdağ to show his support for Mayor Eşkinat, who was released by a court last week on judicial probation and under a travel ban, in a case in which he was accused of insulting Erdoğan by saying “fascist, dictator.”

Lawyers for Erdoğan, who has dominated Turkish politics for more than a decade, have filed more than 1,800 cases against people including cartoonists, a former Miss Turkey and schoolchildren on accusations of insulting him, Reuters reported.

“If they [the CHP] are searching for a dictator, they should look into their past,” Prime Minister Binali Yıldırım said on Tuesday during the Justice and Development Party (AKP) group meeting in Parliament, in reaction to Tezcan’s remarks about Erdoğan.