The ONMS said in a statement that in cases of racism the referee should alert the fourth official who should in turn report the incident to the public security department responsible for policing at games.
"The director of the public order service has the sole responsibility for suspending the match," said the statement.
The ONMS said the decision followed a meeting with the Italian football federation.
AC Milan last week walked off the pitch during a friendly against a lower tier side after Kevin-Prince Boateng refused to play on following racist abuse from a small number of supporters in the crowd. (Reporting by Brian Homewood; Editing by John Mehaffey)