The Professional Fire Fighters Union claims 111 operators would struggle to deal with a fire in a tunnel on the new Northern Gateway route, north of Auckland.
The 7.5km highway opened last month and the Fire Service does not yet have mapping data for it on its communications system.
The union's Auckland president Jeff McCulloch says 111 calls are diverted to other centres if the northern communications centre is busy or down.
He says other operators may not know which fire station to contact without complete information.
However, the Fire Service says operators would still be able to dispatch the right crews because they have general maps for the area.
The $365 toll route was opened at Anniversary Weekend.