The increased security comes in the wake of alleged incidents of Islanders fans mistreating Capitals fans during Game 3 and reports that fans stole seats from the building.
Nassau County Police have already said they will be adding additional uniformed and plain clothes officers around the arena, along with officers on horseback.
"The fact of the matter is you're going to have incidents you wish you didn't have, and you're going to have to respond to them," NHL Commissioner Gary Bettman said. "I think the Islanders have done it appropriately and our security people have been working with the building and Nassau County to make sure inappropriate conduct is both discouraged and dealt with, if necessary."
Game 6 of the series will take place on Saturday at 3 p.m., with the Islanders on the brink of elimination.