The move is in response to the death of St. Louis Cardinals pitcher Josh Hancock in a car crash last week. Hancock was legally drunk when he drove his sport utility vehicle into a tow truck April 29.
"If anything were to happen, (the team's ownership) would be liable," said Will Ohman, the Cubs' player representative. "It's interesting because the guy in the stands can go seven or eight (innings) deep, and because he paid for it, he's the only person liable. That's the legal system."
A police report said Hancock had been drinking before the crash. Cardinals Manager Tony La Russa later said Hancock had been warned a few days earlier about his drinking problem.
The Cubs also banned alcohol on road trip charter flights.