Police sought restraints on new powers given to them under the Act-National "three strikes" violent-crime policy and the Treasury recommended against adopting it, documents show.

Justice Ministry officials warned last week that the policy risked breaching New Zealand's Bill of Rights and international obligations, went against the Government's own policy on the drivers of crime, and impacted on judicial powers.

They also said some juries might not convict criminals, concerned by the unfair consequences if they did, and the group worst affected would be Maori.

Under the amended policy there are certain offences that attract a strike.

Under the National Party policy, a strike offence was a violent crime that attracted a minimum five years' jail.

Concerns were raised when the policy change was announced in January that police rather than judges had the power to decide who would get a third strike, which carries the penalty of serving a full sentence without parole.

In further papers released under the Official Information Act, Police Commissioner Howard Broad offered four options and Police Minister Judith Collins has since adopted a recommendation for officers to refer all prosecutions to the Crown prosecutor before a third strike charge is laid.

The other ideas Mr Broad suggested were for special policy and procedures to be put around third strike charges, a review by senior police before the charge is laid, and a law change requiring cases to go to the Crown prosecutor first.

In a subsequent paper to the Cabinet, the Treasury recommended ministers not agree to the changes. A regulatory impact analysis in the same Cabinet paper said the policy would benefit victims while impacting the most on Maori because of their over-representation in prisons.