Independent Tipperary North TD Michael Lowry says the Government can not rely on his support for the Finance Bill.
Mr Lowry said he had told Taoiseach Brian Cowen and Minister for Finance Brian Lenihan that he disagreed with a number of measures contained in the Bill.
Mr Lowry, who supported the Budget, said he was disappointed there was no exemption for medical card holders from the universal social charge and that retired civil servants would also be expected to pay.
He said bringing forward the date on which self-employed people have to make tax returns was unfair and that families should be allowed to set student fees off against their income.
Mr Lowry was also concerned that a promised 90 per cent tax on the bonuses paid to bankers would not be part of a fast-tracked Finance Bill.
He told RTÉ News at One that it was unlikely he or South Kerry Independent TD Jackie Healy-Rae would support the Bill in its current form.
Mr Lenihan has already said the universal social charge for medical card holders would be reduced from 7 per cent to 4 per cent as the legislation progresses, with self-employed people paying a higher levy to offset the cost.
Mr Lowry said he had honoured his commitments to the Government and that it had supported certain projects and developments in his constituency in return.
He said he had "no obligation or responsibility to support a dysfunctional government" or "half-government". He also criticised the "show stopping antics of the Green Party" and "political opportunism" shown by the Labour Party, which was pushing the Finance Bill through the Dáil but planning to vote against it.
Mr Lowry said he would be discussing his concerns with officials from the Department of Finance later today.
He expected to then inform Mr Healy-Rae of what progress had been made and that they would make a final decision on the Finance Bill this evening.
