In a move that will inevitably fuel speculation the tapes could contain a seriously compromising "smoking gun", lawyers for Sarkozy said they would be filing a request with a Paris court for an emergency injunction against further distribution or publication.
The tapes are thought to contain hundreds of hours of Sarkozy's private conversations with Bruni and close aides. They were recorded by a political adviser, Patrick Buisson, without the couple's knowledge.
Some extracts -- without any really explosive content -- have already been published, by satirical weekly Le Canard Enchaine and news website Atlantico.
Lawmakers across the political spectrum have denounced what they have described as an unprecedented act of treachery and, in some cases, a potential threat to national security.
Also Read
In a statement to AFP, Sarkozy's lawyers said the former president and his supermodel wife had no option but to take legal action.
"The protection of private and secret conversations constitutes one of the foundations of a democratic society and they cannot accept comments made in private being recorded and published without their consent," the lawyers said.
Bruni is heard joking about Sarkozy being a kept man and teasing him that her status as first lady has prevented her from signing lucrative deals to promote wrinkle-creams, unlike actresses Julianne Moore, Julia Roberts and Sharon Stone.
Sarkozy is also revealed to have been rude about some of his ministers.
But that will hardly have come as a surprise to French voters given his reputation for volcanic eruptions. Overall, nothing has emerged so far that is likely to derail his plan to return to frontline politics in time for the 2017 presidential election.