Members of the European Club Association were told by UEFA's chief investigator that many "still need to do their homework" to meet the demands of Financial Fair Play rules, and protect their places in future Champions League and Europa League competitions.
Jean-Luc Dehaene backed his words with action by identifying 23 clubs who face losing their prize money this season for failing to meet financial obligations.
Europa League winner Atletico Madrid and Champions League contender Malaga are among those given until Sept. 30 to satisfy UEFA they have a plan to pay a combined €30 million ($38.4 million) in unpaid players' wages, transfer fees and social taxes.
Dahaene won support from ECA chairman Karl-Heinz Rummenigge, whose members voted unanimously in 2010 to back the UEFA project to curb their spending and loss-making.
"I believe he is right to ask, and to call the clubs to be finally serious," Rummenigge told The Associated Press in an interview, adding that Dehaene's words were "proof that not everybody is respecting the rules."
"We have some black sheep and these black sheep have to wash white," said the Bayern Munich chief executive, whose club is consistently profitable. "These clubs who have been in the auditorium can't misinterpret the wording of Mr. Daheane."
Absent from the meeting was any representative from PSG, which went counter to the increasing UEFA scrutiny and ongoing European economic crisis by spending €250 million ($321 million) on players in the past two offseasons.
In a significant shift of power, Qatar-backed PSG strengthened for its return to the Champions League next week by buying striker Zlatan Ibrahimovic and defender Thiago Silva from seven-time European champion AC Milan.
"I believe AC Milan merit only respect in the football world," Rummenigge said at an earlier news conference on Tuesday. "It is much more difficult to go the way of AC Milan than to go the way of maybe a French club, for example."
Rummenigge later declined to name clubs whose spending he disapproved of.
Since July 2011, UEFA has monitored the accounts of all clubs that qualified for the Champions League and Europa League. Clubs are required to aim toward breaking even on their football-related business, and the worst offenders face being barred from the competitions from the 2014-15 season onward.
However, clubs face immediate penalties for breaking rules relating to "overdue payables."
UEFA showed its intent on Tuesday by confirming the 23 investigations in an unusual move to reveal details of active cases.
Atletico and Malaga are the headline names of those who fell behind making payments at a June 30 deadline to enter the competitions. Sporting Lisbon and Fenerbahce are also being investigated.
"It means that the Financial Fair Play measures are already working. It has some teeth and it works," UEFA general secretary Gianni Infantino said on the sidelines of the clubs' meeting.
Atletico director Clemente Villaverde declined to comment on details of the case.
Last season, UEFA paid the Spanish club €10.5 million ($13.3 million) in prize money funded by Europa League television rights and sponsorship deals.
Malaga can expect to earn at least €20 million ($25.6 million) from the Champions League even if it fails to advance to the last-16 knockout round.
UEFA had already excluded AEK Athens of Greece, Gyor of Hungary and Besiktas of Turkey from this season's Europa League. Other sanctions UEFA can apply to its competitions include ruling newly signed players ineligible and restricting a club's squad size.
Tuesday's list includes teams who were eliminated in Champions League qualifying rounds: Fenerbahce (Turkey), Zeljeznicar (Bosnia), Buducnost Podgorica (Montenegro), Vaslui (Romania) and Partizan Belgrade (Serbia).
The 32-team Champions League group stage kicks off next week, when Malaga plays at home to Zenit St. Petersburg. The Russian club bought striker Hulk and midfielder Axel Witsel from Portuguese clubs last week in deals worth a reported €40 million ($51 million) each.