The Inland Revenue Department (IRD) has admitted it sent out about 600 incorrect tax demands.
It said it was aware that some customers had received a 7 February due date reminder letter with the wrong amount of tax owed on it.
In a statement, IRD group manger of collections David Udy apologised to those who have been affected.
He said it was a matter that was being taken very seriously and if anyone had received a statement they thought was incorrect, they should get in touch with them as soon as possible.
Mr Udy said the IRD processed six million transactions each year and from time to time it did make mistakes.
He said they would be thoroughly reviewing their systems to prevent such an incident from reoccurring.