The Police Association intends to fight plans to introduce performance pay in their latest round of pay negotiations.
An email obtained by Labour MP Kris Faafoi says the police want to take away competency service increments and replace them with performance pay.
The email, which was written by Police Association president Greg O'Connor, says the reason for the change is because management believes some officers are being overpaid by 20%.
Mr Faafoi says the pay dispute is the Government's fault, because it should have seen a shortfall in police spending and accounted for that in the latest Budget.
Police headquarters says the email is not correct, but it is not able to discuss pay negotiations.