It depends on the type of tag being used.
Passive ultrahigh-frequency (UHF) RFID transponders that employ the EPC Gen 2 air-interface protocol are required to have a kill command, enabling a user to permanently deactivate the tag. The kill command requires that a serial number be transmitted to the tag, thereby preventing someone from, for instance, walking into a store with a passive UHF RFID reader and deactivating all tags within the building. Different reader manufacturers have different software applications on their devices that allow a user to transmit the appropriate serial number to unlock and kill the tag.
Other types of passive UHF, high-frequency (HF) and low-frequency (LF) tags do not support the kill command, though some manufacturers may offer this as an option. In that case, the best way to deactivate the tag would be to take a hammer to its chip. You can also place a tag in a microwave oven or zap it with an electric shock, which will overload and blow the microchip’s circuitry. These strategies will also work with passive UHF tags.
—Mark Roberti, Founder and Editor, RFID Journal