The Arizona Republic reports a Maricopa County Superior Court judge is set to hear arguments Friday afternoon from state and county prosecutors that the voter-approved law interferes with federal drug law.
The hearing stems from a company suing Maricopa County over its refusal to provide zoning clearances for a medical marijuana dispensary in Sun City.
The American Civil Liberties Union and its Arizona affiliate have also joined the suit.
Attorneys for the ACLU and White Mountain Health Center say the state is allowed to make policy decisions on medical marijuana.
Arizona is one of 17 states that have approved the use of marijuana for medicinal purposes.