Pierre Berge, president of Le Monde's supervisory board, led the charge on the paper, accusing it of "informing" on the businessmen, politicians, criminals and celebrities named in the so-called Swissleaks files.
"Is it the role of a newspaper to throw the names of people out there? … I don't want to compare it to times past but all the same, informing is informing," Berge, a co-founder of Yves Saint Laurent couture house told RTL radio.
"It wasn't for this that I allowed them gain their independence," the 84-year-old, part of a trio of tycoons that pulled the paper back from the brink of bankruptcy in 2010, added.
After initially shrugging off the criticism the union of Le Monde journalists hit back at Berge Wednesday.
"We forcefully condemn, as on previous such occasions, this intrusion into the editorial content. The role of shareholders is to define company strategy and not to try to lean on the news sense," the union said in a statement.
Le Monde's editorial management also slammed the "attacks by Pierre Berge against Le Monde journalists."
"We assume the editorial choices made during this investigation and during the publication," the editors said, vowing to "scrupulously enforce" the paper's editorial independence.
Berge was not, however, the only one of Le Monde's three main shareholders to quibble with the reporting.
Banker Matthieu Pigasse, who has interests in several French media, also voiced concerns over the reporting, albeit in more measured terms.
"It's true that there is a balance to be struck between disclosing information that is in the public interest" and "falling into a form of fiscal mccarthyism and informing," the head of Lazard investment bank in Paris said, while stressing he was "proud" of Le Monde's work.
The paper's third co-owner, telecoms magnate Xavier Niel, made no comment. The trio signed an agreement with the paper in 2010, guaranteeing its editorial independence.
Le Monde played a leading role in revealing how HSBC's Swiss private banking arm helping clients in more than 200 countries evade taxes on accounts containing $119 billion (€104 billion).
The French paper, which obtained files leaked by a whistleblower, shared them with the International Consortium of Investigative Journalists (ICIJ), which comprises dozens of media organisations worldwide.