French media have been warned not to publish content from any emails allegedly hacked from presidential candidate Emmanuel Macron's campaign team, to prevent the outcome of the vote being influenced.
It comes after Mr Macron's team said it has been the target of a "massive and coordinated" hacking attack ahead of Sunday's presidential runoff.
France's presidential election commission also said it could be criminal offence to republish any campaign data.
Earlier, in a statement, Macron's party En Marche!, which he founded in 2016, said it was hacked a few weeks ago and that the leaked documents had been mixed with false ones online.
It added that whoever is behind the leaked documents is trying to "seed doubt and disinformation" and destabilise the runoff.
Earlier, WikiLeaks tweeted that the leak contained "many tens of thousands" of emails, photos and attachments dated up to April 24.
But it said that it had come "too late" to affect the election results.
There is no suggestion WikiLeaks is responsible for the hack and other tweets from the account also implied that this is not the case.
Emmanuel Macron will duel with the far-right's Marine Le Pen for the keys to the Elysee Palace.
The candidates stopped campaigning at midnight on Friday to give voters a day of reflection before the poll, which has already seen the two parties that have dominated post-war politics cast aside by voters.
Polls suggest Mr Macron, 39, will win comfortably, with the defeated Gaullist and Socialist candidates endorsing him to succeed Francois Hollande with appeals for national unity against Ms Le Pen's Front National.
Mr Macron broke with the Socialists and set up his own movement which he insists is neither left nor right.
The fact neither a Gaullist or Socialist is in the run-off is unprecedented since France adopted its Fifth Republic system in 1958.
Traditionally centre-left wins in presidential polls are celebrated at the Place de la Bastille and centre right triumphs across Paris at the Place de la Concorde.
In a bid to show En Marche! is not aligned to either political side, Mr Macon's team reportedly sought permission to use the Champs de Mars behind the Eiffel Tower on Sunday for what he hopes will be a victory rally.
However permission was refused in order to protect the lawns that are part of Paris's Olympic bid.