A bill to prevent those behind bars from voting passed its first reading yesterday amid heated debate in the House, during which the Green Party were called communists, National's Sandra Goudie gleefully used the word "duh" and Labour's Chris Hipkins found himself in the rather unusual position of agreeing with Hone Harawira.

The Electoral (Disqualification of Convicted Prisoners) Amendment Bill passed under the usual rhetoric from both sides of the House - "soft on crime" versus "dog-whistle politics".

At present prisoners serving a term of three or more years cannot vote. Prior to 1993, when this law came into effect, imprisoned convicts could not vote.

National's Paul Quinn, who submitted the bill, said prisoners had transgressed against society and it was time to consider where to draw "the line in the sand".

Act MP David Garrett said blood had been spilled in some parts of the world, such as England, to secure the right to vote.

When Labour's Charles Chauvel said not every person in prison was necessarily a serious offender, Mr Garrett cried out: "Wrong."

Mr Chauvel continued: "Mr Garrett knows better than the Solicitor-General on this point."

The Greens' David Clendon asked the Government to consider more "rational" approaches than tougher sentences and "populist" policies, which Sandra Goudie interpreted as saying locking up criminals was irrational.

"The Greens' other interpretation is to call the law of locking up criminals extreme coercion. I mean, you know, like, duh. It's about keeping New Zealanders safe."

Mr Harawira said the bill would affect 5000 more prisoners, and questioned the "motivation of targeting people who are already isolated from our society ... except to punish them, to prove how nasty and vicious this society can be ... and to show what a callous and depraved society we really are."