Finance spokesman Pearse Doherty has said that Sinn Féin will not agree to go into Government unless it can abolish the Property Tax.
He says the tax is an unfair penalty on family homes, and ignores people who can afford to pay more.
Speaking at the MacGill Summer School in County Donegal, he said Sinn Féin has always been opposed to the Property Tax in its current form.
"Sinn Féin have been the instigator of many of those motions - and they're only a prelude," he said.
"We have said very clearly - when we're in Government … we will only enter Government if we can get rid of Property Tax, because it's not a right form of tax, in our view.
"We want to increase a proper Property Tax, which is a wealth tax."