Associate Transport Minister Craig Foss says alcohol interlock sentences will soon become mandatory for serious and repeat drink-driving offenders.

He says anyone convicted of two or more drink-driving offences within five years and any first time offenders caught driving more than 3.2 times the legal alcohol limit will be subject to an alcohol interlock sentence.

"Mandatory interlock sentences are a targeted and effective way to help spare families, friends and communities the pain and suffering that inevitably follows each and every one of those crashes," Mr Foss says

"Research shows interlocks reduce reoffending rates by about 60%."

Alcohol interlock sentences have been available as a sentencing option since September 2012. The sentence is one of a range of sentences available to the courts for people convicted of drink-drive offences.

The Ministry of Transport says alcohol interlocks will become mandatory for those offenders who are currently eligible for the alcohol interlock sentence. 

"The Government will also include offenders who are currently subject to compulsory alcohol assessments and indefinite disqualification. As well as the normal criteria that apply for removing an interlock, these offenders will also need a satisfactory alcohol assessment."

Once an offender has received the mandatory alcohol interlock sentence, they need to apply to the NZ Transport Agency for an alcohol interlock licence. Once they have an alcohol interlock licence, they will need to use a vehicle fitted with an interlock for at least 12 months.

The ministry says the interlock can only be removed if the offender has had six months free of violations. 

"A violation is earned, for example, when an offender attempts to start the vehicle with alcohol on their breath, or they attempt to tamper with the interlock. The six-month violation free period can be reduced to three months if the offender obtains a satisfactory alcohol assessment."

After the interlock is removed, the offender must apply for a zero-alcohol licence. The zero-alcohol licence must be held for three years. This means that the licence holder cannot drive with any alcohol in their breath or blood.

A mandatory alcohol interlock sentence will not prevent the courts from giving additional sentences, such as fines and imprisonment, should the circumstances of the offence merit it.