Three water charge protestors, who were jailed last week, are set to refuse fluids from today.
The men stopped eating at the weekend, and decided to step up their action after being transferred from Mountjoy to Wheatfield prison.
They want to be returned to Mountjoy, because it is easier for their families to visit them there.
The men are serving sentences for breaching court orders not to obstruct water meter installations.
In a statement on his Facebook page on Saturday night, Derek Byrne said they began the hunger strike on Friday night, and will refuse fluids if they are not moved back by Monday evening.