Plans to privatise more prisons should be reconsidered after revelations that operator Serco has failed to meet some of its performance targets, Labour says.

Serco has been running Auckland's Mt Eden Prison for eight months and Radio New Zealand has documents which show it was fined $150,000 after a prisoner escaped, two other prisoners were wrongly released and reports on rehabilitation and prisoner wellbeing weren't provided.

The documents, obtained under the Official Information Act, show Serco fell "significantly short" of its prisoner management plan targets, RNZ reports.

Labour's justice spokesman, Charles Chauvel, says Serco also failed to meet drug testing targets.

"The public has a right to expect Serco's performance targets to be met," he said on Friday.

"If it can't meet those targets while it runs new institutions with more operational flexibility than the state system, that should send a strong signal that plans to expand its role significantly via the new Wiri Prison need a rethink."

Mt Eden has just under 1000 beds and the new prison will have about the same number.

"If they can't meet their targets on their existing operation why one earth should we be giving them another 1000 beds in the system to look after," Mr Chauvel said.