Police are now investigating the incident.
RNZ understands the prisoner was a member of the Comancheros gang and the Corrections officers targeted worked at Auckland's Mt Eden prison.
Corrections took two months to respond to an Official Information Act request from RNZ and has withheld most documents relating to the incident, however, National Commissioner Rachel Leota confirmed it occurred on 23 May.
"When Corrections staff were socialising at a bar outside work hours, a bar tab was anonymously left by a member or members of the public for Corrections' staff use," she said.
"Corrections staff did not use the bar tab and departed from the location.
"We are satisfied that the staff behaved appropriately and no breach of our Code of Conduct occurred."