The governor of Mountjoy Prison, Mr John Lonergan, has raised doubts over the merits of a new Government strategy aimed at ridding the State's prisons of drug use.
Mr Lonergan said it would be "ideal" if prisons became drug-free, but he questioned whether this would occur through proposed new policing measures such as mandatory screening.
He noted screened visiting took place at Cloverhill Prison, and "I don't think anybody would claim that Cloverhill Prison is drug-free".
He added: "I have ideas about how it should be tackled, and I do think it is wrong to have about 200 to 250 people at a time in Mountjoy with a very chronic, ongoing drug addiction, and the only thing we can do as a State is to provide methadone maintenance on its own. I do think we should be doing a lot more."
Speaking in the Dáil last week, the Minister for Justice, Mr McDowell, emphasised the Government's commitment to mandatory testing of prisoners and creating drug-free prisons.
However, speaking on RTÉ radio yesterday, Mr Lonergan said unless drug abuse was tackled in the community, "and until we have drug-free communities, we won't have drug-free prisons".
The governor rejected suggestions that he intended to resign over the issue, saying he had "no intention of leaving Mountjoy in the immediate future".
However, he confirmed he would not serve as governor of Mountjoy if and when the prison relocated under the Government's plans.
"It has absolutely nothing in the world to do with policy My position is that at any time over the last six years I could retire legitimately having served my time. Any time in the future over the next nine years I can retire.
"But what I said was I was certainly not going to start over in a new prison at this stage of my career and my life."
As for any perceived disagreement with the Minister, Mr Lonergan stressed his role as a public servant was "to implement policies laid down by the Government".
The Labour Party's spokesman on justice, Mr Joe Costello, said the "stand-off" between Mr Lonergan and Mr McDowell resulted from the Minister's "bull-in-a-china-shop" approach to prison reform.
"Whilst on the face of it the disagreement is about drug testing and contact between inmates and their families, the whole affair calls into question the Minister's methods of reform without consultation or reference to those who have been running the Prison Service for years."
A spokesman for Mr McDowell said the Minister had already discussed the proposals with the prison governors and the Prisons Service.
However, Mr Costello said: "The Minister's attitude to drug testing disregards the fact that 70 per cent of the prison population are already addicted before they enter prison."
