The inquiry's lawyer is arguing that the probe needs documents from Operation Colisee, a widespread investigation into Montreal's Mafia in 2006.
The RCMP has deposited a motion contesting the request, and it was argued Monday in Quebec Superior Court.
The force is arguing on the principle that a provincial inquiry can't compel a federal agency to hand over documents from the case, which was the largest Mafia probe in Canadian history.
The commission had hoped to begin its work in May, but has warned that it could be delayed if the RCMP refuses to provide the documentation.
Time is of the essence: the commission's work is supposed to be completed by October 2013.
Premier Jean Charest called the inquiry under intense public pressure following a series of reports of corruption involving the construction industry, political parties and organized crime.
Lawyers for the police force and the commission have agreed to open negotiations toward a possible solution. A commission spokesman says unless there is a solution, the case will appear again in court on April 18.