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.
In a statement Mr 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.
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.
Mr Adam's statement said: "I am conscious that the legal process involving Tom Murphy has yet to be concluded, naturally full comment should be reserved until that process has ended.
"However let me be clear, everyone has a duty to pay the taxes for which they are liable. There can be no equivocation on this whatsoever
"Those who for any reason have been in default of tax returns need to rectify this and need to ensure that tax returns are in order and in accordance with the law.
"I believe that Tom Murphy has been treated unfairly. All citizens have the right to be judged by a jury of their peers.
"It is extraordinary that a case involving a failure to complete tax returns is heard before a non-jury court. Tom Murphy’s rights have been denied to him.
"There have been many prominent public figures accused of tax irregularities including TDs. They have not been treated in the same fashion as Mr Murphy. Neither have they been labelled as criminals by those media outlets currently writing lurid headlines about Mr Murphy.
"I have been asked if I consider Tom Murphy a good republican. The answer to that is yes," the statement concluded.
Mr Murphy has vigorously contested the allegations against him.