Galatasaray have accused Fenerbahce manager Jose Mourinho of making "racist statements" following a 0-0 draw between the bitter Istanbul rivals.
It was not immediately clear what comments Galatasaray were referring to and former Real Madrid, Manchester United, Chelsea and Spurs coach Mourinho has not responded publicly to the allegation.
Speaking following Monday's league draw at Galatasaray, the Portuguese coach reportedly said the home bench had been "jumping like monkeys".
He also reportedly repeated his criticism of Turkish referees.
The game was refereed by Slovenia's Slavko Vincic, said to have been appointed after a request from both clubs that a foreign official take charge of the high-profile encounter.
In its statement, Galatasaray said it would launch criminal proceedings against the 62-year-old Mourinho.
"Since the commencement of his managerial duties in Turkey, Fenerbahce manager Jose Mourinho has persistently issued derogatory statements directed towards the Turkish people," the club said.
"Today his discourse has escalated beyond merely immoral comments into unequivocally inhumane rhetoric.
"We hereby formally declare our intention to initiate criminal proceedings concerning the racist statements made by Jose Mourinho, and shall accordingly submit official complaints to Uefa and Fifa.
"Furthermore, we shall diligently observe the stance adopted by Fenerbahce – an institution professing to uphold 'exemplary moral values' – in response to the reprehensible conduct exhibited by their manager."
There was no immediate comment from Fenerbahce, who are second in the Super Lig six points behind Galatasaray.