Hartley was sent off during the first half of his side’s 37-17 defeat to Leicester Tigers after Barnes felt the player called him a ‘f****** cheat’.
Saints have come out in support of their captain, who claims he was aiming the insult in the direction of Tigers hooker and England team-mate Tom Youngs.
But the disciplinary panel, chaired by His Honour Judge Jeff Blackett decided otherwise and have handed Hartley a lengthy suspension.
Judge Blackett said: “We cannot get around the fact that Wayne Barnes was certain that Mr. Hartley’s comments were directed at him. Wayne Barnes said that if he had had any doubt in his mind, then he would have given the player the benefit of the doubt.
“In terms of sanction, calling a referee a cheat is an attack on his integrity and contrary to the core values of rugby and therefore we have taken a serious view and provided a serious sanction.”
Hartley was set to travel with the Lions to Australia this summer, but will now sit out the tour, which runs from June 1 to July 6.
He is suspended from today [May 26] until July 6 and from August 17 to August 31 and free to play again on September 1.
In accordance with the Lion tour agreement the six-week tour of Australia represents eight of the eleven weeks suspension because of the tour schedule.
The remaining three weeks of the suspension cover three of Saints’ pre-season matches.