The Tribal Police Department Parity Act seeks to establish parity for Tribal law enforcement agencies by ensuring they have the same access to firearms as Federal, State, and local law enforcement. This legislation specifically amends federal statutes to include Indian Tribes and their departments or agencies in existing exemptions. Key provisions modify Title 18 of the U.S. Code, allowing Tribal law enforcement to be exempt from prohibitions on the transfer and possession of post-1986 machineguns and from restrictions on the transportation, shipment, receipt, possession, and importation of firearms and ammunition. Furthermore, the bill amends the Internal Revenue Code of 1986 to extend firearm transfer and making tax exemptions to Indian Tribes. These changes aim to provide Tribal police departments with the necessary tools and legal standing to perform their duties effectively, aligning their capabilities with other governmental law enforcement bodies.