The Garda Ombudsman is to investigate complaints officers threatened to rape protesters at energy giant Shell's gas project in the west of Ireland.
Two gardai, one a sergeant, were inadvertently taped making remarks about two women activists who refused to give their names on arrest last Thursday at the controversial Corrib scheme in Co Mayo.
A camera the women had been carrying was left recording in the back of a patrol car and allegedly captured the conversation.
Anti-Corrib campaign group Shell to Sea said the women, who do not wish to be named, will be making a formal complaint to the Garda Ombudsman.
"This is shocking and extremely serious. It is very frightening for those of us involved in the campaign," said protest spokeswoman Caoimhe Kerins. "Gardai are the people that women are supposed to trust when they need to report a rape. Gardai are supposed to be responsible for bringing rapists to justice."
Sinn Fein TDs have also said they will ask the Ombudsman to step in. A superintendent from outside the county has been brought in to oversee an internal investigation into the allegations.
A video camera confiscated by officers during the protest at a Shell compound at Aughoose, north Mayo, allegedly recorded officers travelling in a patrol car separate from the arrested women. The conversation includes threats to deport and rape one protester who had refused to give her name.
A line from the 37 minute recording has one garda saying that one of the women "sounds like a Yank or Canadian". A more senior garda, understood to be a sergeant, adds: "She refused to give her name and address and was told she would be arrested". A colleague joins in: "And deported." Before the sergeant says: "And raped."
The women had been detained on a public road about half an hour after one of them had been taken down from the roof of a tractor hired as part of Shell's preparatory work on the gas pipeline at Aughoose. Both women were released without charge and later discovered the recording.
Ireland's Rape Crisis Network Ireland said senior gardai should consider suspending the officers at the centre of the controversy. "We are calling on the gardai to reassure the public that the gardai involved in the inquiry following the recording of rape 'jokes' will not be involved in any sensitive area of duty while the investigation is under way," a spokeswoman said.