Szymon Marciniak also refereed the Champions League semi-final second leg between Manchester City and Real MadridUefa is reviewing the appointment of Szymon Marciniak as the Champions League final referee after he spoke at an event organised by Polish far-right leader Slawomir Mentzen.
Poland's Marciniak, 42, is set to officiate Manchester City's match with Inter Milan in Istanbul on 10 June.
He attended the Everest business conference in Katowice on 29 May.
"I always disassociate myself from expressions of racism, anti-Semitism, and intolerance," Marciniak has said.
Marciniak refereed the World Cup final between Argentina and France in December.
"Uefa is aware of the allegations surrounding Szymon Marciniak and is seeking urgent clarification," European football's governing body said, adding it would make a further announcement later on Friday.
"Uefa and the whole football community abhor the 'values' that are promoted by the group in question and takes these allegations very seriously."
Mentzen, co-chairman of the far right and libertarian Confederation party, has focused on his libertarian economic views in recent times but caused controversy in 2019 when he announced his five-point slogan which was anti-Semitic and homophobic.
Poland's "Never Again" anti-racism association has called on the referee to distance himself from far-right activities.
"Having been an international football referee for many years, I always put fair play and respect for others first and I want to pass on these highest values to others," Marciniak said in a statement to the Onet Przeglad Sportowy website. "I always disassociate myself from expressions of racism, anti-Semitism, and intolerance, which I show in matches I referee.
"I always say stop the hatred, and will promote that the most important thing is to be a good person."
Mentzen said the business conference had "nothing to do with politics", and called the "denunciation" of Marciniak "absurd".
"He [Marciniak] has never expressed any support for my political activities, and to exclude him from refereeing the Champions League final for this reason would be a profound abuse," he wrote on Twitter.
In a letter to Uefa president Aleksander Ceferin, the Polish sports minister Kamil Bortniczuk said the business conference had nothing to do with politics and that the referee had delivered a 45-minute inspirational talk at the conference. Mr Bortniczuk said the referee had no contact with the far-right leader at the conference.
Polish deputy foreign minister Pawel Jablonski said untruthful accusations against Marciniak are "an immense scandal".
The Confederation party has nine MPs in the Polish parliament - Mentzen is not one of those. In recent polls, it has placed as high as third ahead of this autumn's parliamentary elections. The party draws much of its support among young men.
