Fianna Fáil says there is no point in implementing a property tax which people cannot afford to pay.
Weekend reports suggest the government has told the Troika that a valuation-based system will be introduced from next January.
However the Finance Minister Michael Noonan is insisting no details have been agreed by the Cabinet as yet.
Fianna Fáil's finance spokesperson Michael McGrath says people's inability to pay must be taken into account.
"Are they really going to expect the 130,000 families in mortgage arrears to pay a property tax? Are they going to expect people in negative equity to pay a property tax?
"I think that the key issue is the ability to pay and at this point in time, given where the country is at and the very real difficulties people are facing, I genuinely do not believe there is an ability to pay €400 or €500 in many cases."