Investigations of Corrections Department staff have quadrupled in the past five years.
In 2006, Corrections investigated 112 employees in the prison system.
Last year that had increased to 457, figures obtained under the Official Information Act show.
More than half led to disciplinary action, and 18 prison guards were sacked.
Corrections says the increase in complaints looks bad, but it is in line with more prisons, more employees and a push for better staff integrity.
Maori Party justice spokesperson Rahui Katene says the situation is horrifying and a far-reaching inquiry is needed to dig deeper into the department's culture.
