The NBA and the NHL have stepped up security at Chicago Bulls and Blackhawks games.
The teams announced a new policy on Friday that discourages fans from bringing bags to the United Center.
The new rules prohibit all backpacks and hard-sided bags, along with any other bags - including briefcases, luggage, purses and diaper bags - that are larger than 14 inches by 14 inches by 6 inches in size.
Fashion backpack purses as well as single-compartment drawstring bags will be permitted, the Blackhawks said in a statement.
All approved bags are subject to inspection upon entry, the team continued, adding that the United Center is unable to check or store prohibited items during the game.
The new guidelines also apply to all NBA team venues, according to the Bulls.