The commission said the leaked data came from Macron’s “information systems and mail accounts from some of his campaign managers”.
It said “a significant amount” of leaked data had been “fraudulently” obtained and that fake news has probably been mingled in with it.
A spokesman for Macron’s party said: “This operation is obviously an attempt at destabilising democracy, as has already been seen in the US during the last presidential campaign.
“The ambition of the authors of this leak is obviously to harm the En Marche! movement within hours of the second round of the French presidential election.”
As much as 9 gigabytes of data purporting to be documents from the Macron campaign were posted on a profile called EMLEAKS to Pastebin, a site that allows anonymous document sharing.
The French election commission said in a statement: “On the eve of the most important election for our institutions, the commission calls on everyone present on internet sites and social networks, primarily the media, but also all citizens, to show responsibility and not to pass on this content, so as not to distort the sincerity of the ballot.”
Vitali Kremez, director of research with US-based cyber intelligence firm Flashpoint, believes a hacking group linked to Russia’s military intelligence directorate was behind the link.
“If indeed driven by Moscow, this leak appears to be a significant escalation over the previous Russian operations aimed at the US presidential election, expanding the approach and scope of effort from simple espionage efforts towards more direct attempts to sway the outcome.”
The leak emerged as polls predicted Mr Macron, a former Rothschild investment banker and economy minister, was on course for victory over far-right leader Marine Le Pen in Sunday’s election, with the last surveys predicting a comfortable election win later today.
Mr Macron’s campaign previously complained about attempts to hack its emails in January, blaming Russian interests in part for the cyber attacks but the Kremlin denied it was behind any such attacks.
President François Hollande was defiant in response to the attack and acknowledged that there had been a worry after alleged hacks in other election campaigns.
The Socialist President said: “We knew that there were these risks during the presidential campaign because it happened elsewhere. Nothing will go without a response.
“If there has been any interference or appropriations, there will be procedures which will begin. We need to let the investigations happen.”