The details came to light when one blogger approached by PR firm Burson-Marsteller published the e-mail exchange.
Burson had been touting stories on behalf of an unnamed client about the Google service Social Circle.
Blogger Chris Soghain did not want to pursue the story and later released the e-mails he had exchanged with Burson.
When the e-mails were published there was a mass of rumours about who the client could be, with Microsoft and Apple in the frame.
Richard Merrin Manging director, Spreckley PRLet's not forget we are talking about two companies that have spent billions in positioning themselves as 'nice, cuddly, sandal-wearing, Californian surfer dudes'”
Facebook has confirmed that it used Burson-Marsteller to expose things which Google was doing that "raised privacy concerns".
Burson told Mr Soghain, among others, that "the American people must be made aware of the now immediate intrusions into their deeply personal lives Google is cataloguing and broadcasting every minute of every day - without their permission."
A Facebook spokesman later told the Daily Beast that it resented Google's attempts to use Facebook data in its own social networking service.
It is a very public play-out of two net giants who have become bitter rivals as they fail to agree on ways to share data.
Both have faced scrutiny over their privacy policies.
Tactics like this are never a good idea, said managing director of Spreckley PR, Richard Merrin.
"I am just trying to imagine the conversation that took place between someone at Facebook and the PR agency in question. I always advise clients that the one thing they must not do is attack the competition," he said.
"This alleged PR smear campaign is the latest highly public example of what many in the industry believe to be the biggest grudge match going in corporate America," he added.
While the revelations will be highly damaging for Burson-Marseller, they will do little for Facebook's image either.
"Let's not forget we are talking about two companies that have spent billions in positioning themselves as 'nice, cuddly, sandal-wearing, Californian surfer dudes.' This has in fact resulted in blowing that carefully constructed image out of the water," said Mr Merrin.
Both Facebook and Google declined to comment further on the story.