Ashton, 24, sparked a brawl that ended in the dismissals of Northampton flanker Tom Wood and Tuilagi after he pulled the Tigers winger into touch by his locks.
The ban lasts until January 3 and rules Ashton out of the Saints' crucial Heineken Cup clashes home and away against Castres and their Premiership games against Bath and Newcastle.
The Rugby League convert should still have plenty of time to return and claim his place in England's RBS 6 Nations squad but will be kicking his heels until the New Year.
"We accepted that this [incident] started by accident but it became clear that at some stage Chris Ashton knew what he was doing," said a Rugby Football Union disciplinary panel chaired by Judge Jeff Blackett.
"If you pull somebody by the hair there is an element of denigration and this act was a catalyst for a mass brawl that resulted in two red cards and significantly affected the image of the game.
"Without any laid-down guidance on sanction, we have aligned the offence to that of spitting and reduced the entry-level points to that of three, six and ten weeks for low, mid-range and top end respectively.
"This was a mid-range offence but we have reduced the sanction by two weeks based on the player's good record and conduct at the hearing."
Tuilagi and Wood both escaped further punishment after their red cards however Northampton flanker Phil Dowson was suspended for two weeks for a dangerous tackle on Alex Goode in the match against Saracens the weekend before.