National Party Leader John Key has released a letter he sent today to the other political parties in Parliament seeking support for his amendment to the anti-smacking bill that the Greens have declined to back.

"Parliament should offer proper guidance for the authorities on the anti-smacking bill," says Mr Key.

"I was deeply disappointed and frustrated at the unwillingness of the Greens to compromise in any way at the meeting with Sue Bradford yesterday.

"Good parents want to have confidence that they will not be criminalised by this legislation. I believe that most MPs do not want to criminalise good parents doing what is one of the hardest jobs.

"I will not give up and am writing to all other political parties in Parliament to seek their support for my amendment.

"National's compromise leaves the bill's purpose clause unaltered but provides guidance to the authorities so that light smacking of a 'minor and inconsequential' nature would not result in prosecution.

"This amendment will reassure good parents that they will not be criminalised by the new legislation - rather than relying on police procedure to avoid investigation and prosecution.

"It is unfair to rely on the police to exercise discretion to make the legislation work simply because Parliament lacks the courage to codify the law in the way we expect it to be enforced.

"I hope that other parties can consider this amendment in that light and support it. I am prepared to meet representatives of any party that wants to discuss this issue."

Click to download letter to political parties on National's Section 59 amendment