Two Christchurch surgeons found by a majority of the Court of Appeal to have avoided their tax obligations were on Monday taking their case to the Supreme Court.
In February, last year the IRD asked the Court of Appeal to overturn an earlier High Court decision which had ruled in the surgeons' favour.
Ian Penny and Gary Hooper had formed companies and employed themselves. The IRD said their companies paid them salaries lower than the market rate payable to someone with similar skills, which amounted to tax avoidance.
In their judgement released in June last year, two out of the three Appeal Court Judges ruled in favour of the department.
However in a dissenting judgement, Justice Ellen France said not all arrangements which produced a tax advantage would constitute tax avoidance.