Sinn Féin leader Gerry Adams says he still considers Thomas 'Slab' Murphy to be a good republican, and says he has been unfairly treated.
Mr Murphy, a prominent republican, was convicted of tax evasion during the week.
The 66-year-old, who lives in Hackballscross, Louth, did not file returns for his farming activities between 1996 and 2004.
In a statement Gerry Adams said that it is extraordinary that a case involving a failure to complete tax returns was heard before a non-jury court, and that Mr Murphy's rights have been denied to him.
Though he said that "everyone has a duty to pay the taxes for which they are liable," he added that many prominent public figures, including TDs, have been accused of tax irregularities without being treated in the same fashion as Mr Murphy.
"They have not been treated in the same fashion as Mr Murphy," he said. "Neither have they been labelled as criminals by those media outlets currently writing lurid headlines about Mr Murphy."
Responding to Adams comments, Fianna Fáil leader Micheál Martin called them "extraordinary" and said they show that Sinn Féin are not fit for Government.
He said it is another example of Sinn Féin not facing up to paramilitary criminality, and that the party is "more interested in protecting [its] own than enforcing the rule of law."