The inmates of the Welikada, Kalutara and Vavuniya prison are demanding that they be charged for their crimes or be released.
The fast began last week with the participation of 80 inmates of the Welikada prison but the number rose to 234 over the weekend with prisoners from two others prisons also joining the protest.
Tamil National Alliance (TNA) parliamentarian M.A. Sumanthiran said that most of the prisoners have been in jail for over three years without being charged.
He said that a special discussion will be held on Monday with the prison authorities regarding the long term detainees.
The European Union (EU) had earlier this month called for a fair trial for long term detainees in Sri Lanka.
Chair of the European Parliament Delegation for Relations with countries in South Asia, Jean Lambert had said that the EU parliament’s position on long term detainees in Sri Lanka is that they should be either charged or released.
Several hundreds of suspected LTTE cadres and other political prisoners are in Sri Lankan prisons, some of whom have not faced trial or a charge years or months after they were arrested.
Most of the prisoners were arrested while emergency regulations were in place during the war between the rebels and the military.
The war ended in May 2009 with the defeat of the rebels. Most of the emergency regulations were also subsequently lifted.