It is believed that Mr Studdart was asked to leave the school.
Last month the school's principal Richard Stanton wrote comments in the school newsletter opposing The Marriage (Definition of Marriage) Amendment Bill.
A Facebook page, "Support Gay Rights at Pom" was set up on which many pupils expressed outrage at their principal's comments. Some planned a protest at the school by wearing rainbow ribbons or armbands to show their support for gay marriage.
The next day Mr Studdart said he was told he was being suspended for supporting the protest.
"It was said I breached the school uniform policy by encouraging students to wear a rainbow wristband to support the rights of the gay community," he said last month.
His union, the PPTA, today said it was not its policy to comment on individual cases.
"It's complicated when teachers take up jobs at schools with special character because it does involve a certain amount of commitment to the principles of that special character - provided they do not breach human rights or provisions under the employment relations act - and there can be tension in the way that operates," PPTA president Robin Duff said.
New Zealand Catholic Education chief executive Pat Lynch said he would not make comment about this particular case.
"More broadly, Catholic preaching on same sex marriage is part of the church's moral preaching so if you take up employment in a Catholic School you're obliged to support the religious and moral preachings because that's what the school stands for, whether you believe in it or not."
Sometimes employees had to agree to disagree if they wanted to keep their job, he said.
Blair Scotland, a senior associate of law firm Chen Palmer specialising in employment matters, said an employer would have trouble justifying drastic action like dismissing someone when it was about a fundamental human right.
"How the employer justifies its actions is going to be key. It's going to be very difficult for an employer to say 'this employee's belief ... I don't agree with and therefore I'm going to impose my views and I'm going to sack this person because of the particular views'," he said.
The reasoning that Mr Studdart breached uniform policy by letting his students wear colourful wristbands would be "very questionable", Mr Scotland said.
Marriage Equality spokesman Conrad Reyners said gay marriage was an issue that youth in particular cared about and Mr Studdart's support should be applauded.
"It's great that he showed leadership and supported his students, particularly as youth and queer youth in particular are often featured in horrible statistics involving youth suicide or self harm."
A letter from the board stated Mr Studdart's teaching practice was not in question.
Principal Richard Stanton said it was "innovative and engaging" and he was highly regarded by his students.
