The SIPTU representative who sat on the Commission for Taxation has described the body's proposals on tax reform as "unfair".
Brendan Hayes, the union's vice-president, refused to sign off on the report that was published by the Government yesterday.
The document recommends a range of new taxes, including a property tax, carbon taxes, water charges and the taxing of child benefit payments.
It also says these measures should be offset by tax reductions elsewhere to ensure the overall burden of taxation does not increase.
Mr Hayes says he fundamentally opposes this commitment to a low-tax ideology because it prevents the development of decent infrastructure and public services.
He says Ireland has one of the most unequal societies in Europe and the Commission for Taxation's proposals would do nothing do address this situation.