When Peter Wirtz sold his food-service contract at the United Center in 2009, it marked an unusual split within the private, wealthy family whose assets include half of the stadium, the Blackhawks, a giant liquor distributorship and real estate.

The sale of the stadium’s Bismarck Enterprises operation to Levy Restaurants meant that Mr. Wirtz, 50, no longer had a reason to routinely be around the hockey franchise he grew up with — severing a major tie to the most public piece of the family empire, one now controlled by his brother Rocky.

The rift between the brothers has spilled into a court battle over another part of the family holdings: ownership of a lucrative beer distributorship worth millions of dollars. It is the only unresolved disposition of family assets left after the death in 2007 of family patriarch Bill Wirtz, and it has siblings and extended family, who also are shareholders, choosing sides.

Late last week, three sisters and shareholders — Gail Wirtz Costello, Karen Wirtz Fix and Alison Wirtz — joined a petition Peter had filed last month against Rocky.