The National Party is seeking an assurance from the Government that the mistaken release of a Black Power gang associate just 10 days into a six-month sentence will not occur again.
Christchurch prisoner Faalilo Faalilo, 33, was released from Christchurch Men's Prison on Monday after a "computer cock-up".
The father of five was told on Tuesday he had to return to jail.
Faalilo was jailed for driving while disqualified and excess blood alcohol.
Faalilo said his surprise release had delighted his children, but now he had to explain to them why he had to return to prison, the Press newspaper reported.
He said he asked wardens why he was being released early but was not given a clear answer.
The Corrections Department has launched an investigation.
Christchurch Men's Prison manager John Roper said Faalilo's sentence had been miscalculated, but picked up through a double-checking procedure.
National Party corrections spokesman Simon Power said that was hardly reassuring.
He said Faalilo had been described as "extremely violent" and his release meant there was a hole in the system through which almost any kind of criminal could be released.
Faalilo was acquitted of attempted murder in 1999 for the shooting of Oliva Twist Sitani in a shop doorway in Lichfield St, Christchurch, in October 1998.
"That hole is so bad that when Faalilo apparently asked why he was being released early, he says he didn't get a clear answer - he blew the whistle on himself and they still didn't wake up," Mr Power said.
"We were fortunate that the slackness in the system didn't have disastrous consequences - we may not be so lucky next time."
He called on Corrections Minister Damien O'Connor to assure the public the problem had been fixed.
A spokesman for Mr O'Connor said it was an operational matter being handled by the department.
Mr Roper said prisoner sentences were complex to calculate.
"We deal with over 12,000 prisoners each year. Unfortunately from time to time we may get these calculations wrong, which has happened in this case."
