Stopping prisoners voting has been described as an assault on fundamental human rights.
"Jailhouse lawyer" Arthur William Taylor has fought through the High Court, Court of Appeal, and now the Supreme Court, against the 2010 law which banned all prisoners from voting in elections.
Previously prisoners could vote if they were serving a term of less than three years.
Today Barrister Richard Francois, acting alongside Taylor, said voting was one of the most fundamental rights.
"For some it's the most fundamental. For others, it doesn't matter.
"You can take away that right with legislation, without restriction. My clients say that's an assault on fundamental rights.
"The right to affirm one's allegiance to politics and to society, and the power to recall a Government to its duties and obligations are cornerstones.
"Decisions of government affect all our life. Decisions of family, of education, a home to rear one's children.
"All of that dependent on voting. And all of that can be taken away by a Government that doesn't respect its people."
Francois said that Government was only by the consent of its people, and Parliament couldn't be allowed to "do whatever it likes" to act against its people.
Taylor, appearing via audio-visual link, told the Supreme Court Justices that he became involved in the case for the public interest, rather than personal reasons.
He said that being a prisoner made him part of a vulnerable minority group, so he tried to promote that group's interests.
Taylor is currently serving a 17-year sentence in Auckland Prison at Paremoremo on a variety of drug and violence charges. So even if the ban was reversed, he would not meet the prisoner voting criteria of being imprisoned for less than three years.
Yesterday the Crown also staked its argument on defending our democracy, but for the opposing argument.
Solicitor-General Una Jagose said the Court risked undermining New Zealand's democratic foundation if it formally criticised the ban on prisoner voting.
She said that while courts had the power to clarify or interpret laws, they did not and should not have the power to create them.
In previous decisions on this case, the High Court declared the voting ban was inconsistent with the Bill of Rights Act, because it infringed on the rights of New Zealand citizens to vote.
The Court of Appeal upheld that decision.
The Supreme Court is now the final legal option.
The Justices have reserved their decision.