A senior Corrections officer has been sacked after allegedly having sex with a colleague on duty in an Auckland prison high security area.

Mohammed Ifraz was fired in August after Corrections found out about the "sexual activity" that took place for six months in the Auckland Regional Women's Corrections Facility.

He is fighting the dismissal and has taken the case to the Employment Relations Authority, which released its decision today not to reinstate Mr Ifraz while the case is being investigated.