A prison officer has been arrested on suspicion of smuggling drugs into Maghaberry.
Police arrested the 50-year-old woman at the Co Antrim jail on Monday.
She is under investigation for the alleged smuggling of class A and B drugs, as well as a mobile phone.
It is understood the officer works in Braid House, a 120-bed unit which houses life sentence inmates.
The Prison Service said that an officer was removed from duty this week following the police investigation.
Sources at maximum security Maghaberry said two police officers arrested the woman “on the landing” of the unit on Monday.
A PSNI spokesman said: “A 50-year-old female was arrested on suspicion of a number of offences including possession and supply of class A and class B controlled substances following an incident at HMP Maghaberry, Lisburn, on Monday, April 21.
“She has been subsequently released on police bail pending further enquiries.”
The Belfast Telegraph understands the woman, who we have agreed not to name because of security concerns, is contesting the allegations.
Last year the Prison Service announced a major crackdown on drug abuse, joining forces with
the PSNI to reduce the supply and demand of drugs in the jail.
In one week 11 prisoners and three visitors at Maghaberry were caught with illegal substances. The problem of drug abuse was also investigated in two reports by the Prisoner Ombudsman, who linked the deaths of two prisoners at Maghaberry to the availability of illicit substances and prescription medication.
The jail is getting ready to trial the UK's first dedicated prisoner substance abuse rehabilitation unit. Up to 15 prisoners with addiction problems will have access to intensive help through 12-week programmes at the new unit in Glenn House on the Maghaberry site.
Prison Officers' Association chairman Finlay Spratt declined to comment on the officer's arrest while the police investigation is ongoing.
Class A drugs include heroin, cocaine, ecstasy and LSD. The maximum sentence for possession is up to seven years in prison or an unlimited fine (or both). The maximum sentence for intent to supply is up to life in prison or an unlimited fine (or both). Class B drugs include speed and cannabis. The maximum sentence for possession is up to five years in prison or an unlimited fine.