Corrections Minister Sam Lotu-Iiga has defended the past ranking of privately run Mt Eden Prison as the best in the country, saying it was based on its record at the time.
Mt Eden Correctional Facility plummeted from first place to last place in the most recent prison league tables, which are updated every quarter.
The remand prison had topped the table of 17 prisons since the rankings were introduced three years ago.
The jail was managed by British-based company Serco, though the Corrections Department took control of the facility in July following reports of widespread violence and drug use among inmates.
Mr Lotu-Iiga has previously said that Mt Eden's "exceptional" ranking showed that private management of prisons was working.
Asked today about his comment, he told reporters: "I had confidence when they were at the top. Clearly they've gone down. That was subject to the information that I had at that time."
Later, under questioning in Parliament, he said: "I stand by that statement based on the facts that were given at the time. I made that statement in May of 2015."
Labour's corrections spokesman, Kelvin Davis, said today that Serco's problems had been known for some time, but were not formally recognised until they were publicised by the media and Opposition MPs.
"Mt Eden Corrections has gone from top of the table to the bottom in the blink of an eye and I'm concerned that the minister wasn't getting all the facts until we held him to account," he said in a statement.
He also questioned why the Government's penalties for Serco were not harsher. Under its contract, Serco has access to bonuses worth $315,000.
"That's not punishment," Mr Davis said. "That's just not getting a bonus."
Mr Lotu-Iiga said the Government had to honour its original contract with Serco. "The amount is based on the contract that was signed at the time," he said.
Serco, which also runs Wiri Prison, is entitled to $1.2 million in performance-related bonuses each year, but faces deductions for failing to reach targets such as eliminating violence and escapes.
The reports of "fight clubs", extreme violence and drug use at the Mt Eden prison are now being investigated by the chief inspectorate for prisons.
A report was due to be released before the end of the year but this has been delayed because Serco is challenging the findings in court.
Mr Lotu-Iiga said he did not know when the report would be released.