According to the commercial TV station POP-TV, Joras and his attorney Danijel Starman filed the lawsuit with a court in Koper, Slovenia.
"The lawsuit is not part of the election campaign, it was written at a time when Joras was not running for the parliament," Joras and Starman said.
The lawsuit was filed due to Mesic's statement carried by the Slovene media in which Mesic called Joras a "court jester in the service of somebody else".
Joras also claims that Mesic had suggested that he "leave the territory he lives on".
He claims that he intended to file the lawsuit after the elections, but changed his mind after the latest Croatian-Slovene border incident which happened near his house on Wednesday.