The prison population has surged by hundreds since Christmas, just as an entire high-security complex was destroyed in mayhem at Waikeria.
"If the muster continues to increase, we're going to have difficulty finding the right beds," Corrections Association president Alan Whitley said today.
The Department of Corrections said it was normal for the muster to rise at this time of year, for reasons including courts closing during summer holidays.
But from December 29 to January 3, Waikeria experienced the longest, most damaging New Zealand prison riot in decades.
A department spokesman said the prison population on January 12 was 8,739.
The release of some eligible prisoners before the December 15 to January 5 holiday period also affected muster numbers.
The Parole Act gives Corrections discretion to free some eligible inmates in early December if prisoner statutory release dates fall within the holiday period.
A Waikeria complex with capacity for 251 prisoners was wrecked in the riot.
Police are yet to charge anyone in relation to the fires and disorder at the high-security complex.
Whitley said it would not be surprising if a complex investigation occurred.
"It's clearly going to take a while to get the charges."
He was confident charges would eventually be laid.
"No-one's going to let it slip under the radar."
The spokesperson said on Wednesday that there was no issue regarding lack of capacity in the prison network following the Waikeria Prison riot.
"The prison population peaked at 10,820 in March 2018. Since March 2018 the prison population has dropped significantly and today's figure is 8,738.
"Currently there are over 1000 additional beds available in the prison network, without the beds currently being added through the modular unit project.
"The decrease in prison numbers prior to Christmas and the subsequent increase over the Christmas period is something we face every year and is not new to us. Our staff understand this and are experienced and well prepared to manage any fluctuations in the population."
Prison reformist Sir Tā Kim Workman today said an independent review of Waikeria and broader prison estate problems was needed.
"It would be great to see an independent group do the work, probably a well-known QC, probably someone who's prominent in Te Ao Māori" (the Māori World).
He said the review team should also include someone familiar with the criminal justice system.
Workman said a thoughtful approach would be needed.
"The whole thing is in danger of being politicised to the point where people will feel unable to move forward."
He said New Zealand jails had long-standing problems with racism, high levels of Māori incarceration, and young inmates being pressured to join gangs.
"It requires courage in terms of political leadership, that courage to stand up like Andrew Little did at the beginning of his term as Minister of Justice and say: The system is stuffed, racism is inherent in the system."
Minister of Corrections Kelvin Davis described the Waikeria chaos as an inexcusable riot involving mostly Mongol and Comanchero gang members.
Last Sunday, he said Corrections would review how the situation unfolded and escalated.