Turkish Süper Lig leaders Galatasaray said they will "initiate criminal proceedings" and report Fenerbahçe manager Jose Mourinho to FIFA and UEFA over what they call "racist statements."
The move comes after the two sides played to a 0-0 draw in a tense league match in Istanbul on Monday night.
Mourinho had welcomed the appointment of a non-Turkish referee, with Slovenian Slavko Vinčić chosen to officiate. After the match, Mourinho made a point of praising the referee, highlighting the fact he was not from Turkey.
"The performance of the referee was a top performance," Mourinho told his postmatch news conference.
"Anyone, not just from this country but also abroad, watched a big football match. I think the man responsible for that was the referee.
"I went to the referee's dressing room after the game. Of course, the fourth official was there, a Turkish referee. And I told him [the referee], thank you [for coming] here.
"I turn myself to the fourth official and I told [him] this match, if you are the referee ... would be a disaster. When I say him, I say the general tendency."
Mourinho was also asked about an incident early in the game involving his 19-year-old defender Yusuf Akcicek, to which he said: "Again, I have to thank the referee because with a Turkish referee after the big dive and the first minute and their bench jumping like monkeys on top of the kids.
"A Turkish referee would have [given Akcicek] a yellow card after one minute, and after five minutes I would have to change him."
Galatasaray responded with a statement: "Since the commencement of his managerial duties in Türkiye, Fenerbahçe manager Jose Mourinho has persistently issued derogatory statements directed towards the Turkish people.
"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 Fenerbahçe -- an institution professing to uphold 'exemplary moral values' -- in response to the reprehensible conduct exhibited by their manager."
Mourinho has been critical of the officiating in Turkey this season. In January, he said there was a "toxic" environment around referees in the Süper Lig.