Labour could face a legal bill as high as £8 million over the leak, which could bankrupt the party, according to the sources.
Corbyn loyalists have claimed the leaked document shows how "Blairite" officials in the party actively worked against him and prevented Labour winning the 2017 General Election.
Party moderates argue the document was leaked by supporters of Mr Corbyn in an attempt to distract from the mishandling of antisemitism complaints.
Mark Lewis of law firm Patron Law, who is representing 20 of the people affected, said: “If this bankrupts the Labour Party or individuals, so be it. Actions have consequences.
“There are lots and lots of claims. There are claims under the Data Protection Act, there are claims for breach of confidence or invasion of privacy and there are claims for libel."
