Public Expenditure Minister Brendan Howlin says legislation cannot be brought in to reduce pensions of retired politicians, as they are constitutionally protected.
It comes after the Tánaiste Joan Burton said they should consider giving back the pension hike.
Pensions were reduced in 2009 through the FEMPI legislation.
Former Taoisigh, including Bertie Ahern and Brian Cowen, are in line to receive a €2,000 increase on their €134,000 pensions next year.
However, amid calls for politicians to hand back some of their payments, Brian Cowen says he will not accept the increase.
Minister Howlin said, although he would like to tackle the issue of large pensions, a cap cannot be brought in.
Tánaiste Joan Burton says politicians getting large pensions should give something back.
She said: "I just think that they should probably consider their position, because in most cases the pensions are very significant.
"I certainly think so after the different sacrifices which different people have made right around the country over the last six years.
"I think it would be an appropriate action by the politicians."