The action, taken jointly with her husband Jean-Louis Brochen, accuses Francis Néri of defamation.
Néri, who is 71 and lives in Strasbourg, wrote on his blog, Le Systémicien, that he has been requested to appear in a Paris court on September 12th.
Aubry is currently running in the Socialist party primary race to choose its contender for the presidential elections to be held in April and May 2012.
The blog in question appeared on July 11th and made a number of remarks about the relationship between Aubry and her husband as well as about her health. The blog also claimed her husband, a distinguished French lawyer, is a secret Islamist radical. The couple deny all the comments made about them. Néri said he had taken the comments from other sites.
Interviewed by radio station France Info on Tuesday, Néri said the legal action was a "shock." Speaking of Aubry, he said "I have the feeling she thinks I'm just some little guy she can go after without any risk."
Aside from her legal dispute, there was bad news for Aubry on Tuesday when an opinion poll in newspaper France Soir showed her main rival, François Hollande, extending his lead against her.
Among Socialist party supporters, 48 percent said they would like to see Hollande as the party's presidential candidate while 34 percent preferred Aubry, a drop for her of 6 points in one month.