The league made the announcement Monday night, hours after Pacioretty had a hearing over the phone with NHL disciplinarian Brendan Shanahan.
Pacioretty struck Letang in the head with his shoulder with 3:14 left in the third period of Montreal's 4-3 overtime loss to Pittsburgh on Saturday. Letang was bloodied and sustained a broken nose, but he returned to the game and scored the winning goal.
Pacioretty, who wasn't penalized during the game for the hit, will sit out Wednesday at Anaheim, Thursday at San Jose, and Saturday at Los Angeles and will lose $26,351.34 in salary.
He is eligible to return Dec. 6 against Columbus.