Officials in Mountjoy Prison are investigating a protest yesterday morning in which up to 100 prisoners threw the contents of their toilet buckets over a landing.
The prison's governor, Mr John Lonergan, said the "minor and peaceful" protest in B wing was over new visiting procedures which were designed to reduce the amount of drugs smuggled into the prison.
Visitors to Mountjoy are now required to bring photographic identification with them in order to gain admittance, and prisoners must submit a list of six people expected to visit them regularly.
Those involved in the protest were locked in their cells all day and their privileges were withdrawn. A spokesman for the Prison Service said the regulations would protect "vulnerable" prisoners who were being bullied into taking visits from people they didn't know and forced to act as drug couriers.
"The protest was unexpected. The measure was designed to protect prisoners as well as staff. There was a misunderstanding amongst prisoners," the spokesman said.
There were mixed feelings about the new security measures among visitors to the prison yesterday.
Standing at the prison gates. Grace (19), who wasn't allowed by authorities to visit her boyfriend because of the trouble, said she thought the rules were acceptable.
"My boyfriend only has four names to visit him anyway, so it won't bother him," she said.
Another woman who was visiting a relation said the rules were "ridiculous".
"It's not fair for people who aren't on drugs. Now their friends and relations have to be worrying about carrying ID just because of some addicts," she said.
A father who had come with his wife and children to visit a relative said it was "wrong".
Children will not have to bring photo ID as the new regulations only apply to adults.
The Prison Service spokesman said the moves were aimed at minimising the "creative ways prisoners can manipulate the rules in order to bring in drugs".