Michel Platini led UEFA has imposed its first financial fair play sanctions by temporarily withholding prize money from 23 clubs for failing to comply with the rules.
Europa League winners Atletico Madrid, Malaga, Sporting and Fenerbahce are among those under scrutiny.
Clubs face further investigation because of overdue payments to other clubs, employees or tax authorities.
Teams playing in all Uefa club competitions have been monitored since the start of the 2011/12 season.
The are tasked with breaking even in 2012 and 2013 and being assessed during the 2013/14 season.
European football's governing body introduced the rules to force clubs to operate within their means.