Steaua Bucharest, Debrecen and Maribor have all been hit with partial stadium bans, along with FC Chikhura Sachkhere who have been given the same punishment for an incident in Europa League qualifying.
"The fight against racism is a high priority for UEFA," said a statement on UEFA's website.
"The European governing body has a zero-tolerance policy towards racism and discrimination on the pitch and in the stands."
Debrecen were punished following incidents in their match against Cliftonville in Hungary on July 22, while the bans for Steaua and Maribor relate to their matches against Stromsgodset and HSK Zrinjski respectively the following day.
Chikhura Sachkhere played Bursaspor on July 24.
All four clubs will be required to close specified sections of their stadiums for their next European match.
Steaua are due to host Kazakh side Aktobe in the third round of qualifying on Wednesday night after a 2-2 draw in the first leg of their tie, while Chikhura will host Neftci in the third round of Europa League qualifying on Thursday with their tie still goalless after 90 minutes.
Debrecen and Maribor are both away this week as they seek to reach the Champions League group stage, with Debrecen 1-0 on BATE Borisov as they head to Belarus and Maribor leading Maccabi Tel Aviv 1-0 ahead of their second leg.