U.S. banks that must comply with the proprietary-trading ban known as the Volcker rule are facing inconsistent future demands from the five agencies responsible for enforcing it.

Even before the final version is released next week, current and former regulators and bank lawyers predict an uneven approach on enforcement because of differences in style and jurisdiction between the three U.S. regulators that police banks and the two agencies that monitor markets. For many banks, how enforcement is handled could wind up being more important than the language in the 1,000-page text.

"How supervision and enforcement of the Volcker provisions are handled among the five agencies is one of the most important and potentially complicated practical aspects of implementation," said Julie Williams, who was general counsel for the Office of the Comptroller of the Currency before joining consulting firm Promontory Financial Group LLC. The rule could leave multiple regulators targeting the same activity in a single firm in different ways, she said.