Catholic Archbishop Christopher Prowse defends anti same-sex marriage pamphlet in schools

The 18-page 'Don't Mess With Marriage' document urges members of the community to write to their federal members to oppose broadening marriage laws at a "moment in our nation's history" where the church faced a "struggle for the very soul of marriage".

As backlash over the pamphlet continues, an online petition has begun calling for the distribution of the "humiliating and degrading" "anti-LGBT propaganda" to cease in schools.

The mother of a Merici College student who received the pamphlet, Tanya Howell, said she was shocked when she found out her daughter, year 12 student Maddison Fisher, was handed the booklet during a school assembly on Thursday.

"It's quite obvious that they are discriminating against gay Catholic students that attend the school," she said.

"I understand that the Catholic Church doesn't approve of homosexuality and gay marriages but they're out of step with public opinion."

Archbishop Prowse was unavailable for comment on Friday, but in a statement said the church distributed the pamphlet to schools and parishes to "protect that which humanity has given us".

"I understand that this is an emotive, hot button issue and we believe, like most civilisations over the millennia and all major religions, that marriage is at the very centre of good living and good life," he said.

"To re-define what marriage means is not an inconsequential moment in our history.

"We wanted to make a contribution to this discussion."

Ms Howell said Maddison was upset to receive the pamphlet and posted a picture on social media which her Sydney-based gay brother Jay Fisher saw.

"It's hard enough for gay people living with the bigots… they are discriminated against as much as society is changing," Ms Howell said.

The booklet was distributed across 56 Catholic primary and secondary schools to 25,000 students in the archdiocese as of Tuesday, Archbishop Prowse told the ABC.

The pamphlet said the Catholic Church "opposes all forms of unjust discrimination" but asserts that "pretending" same-sex relationships were marriages was "not fair or just to them".

"We all know and love people with same-sex attraction," it said.

"They need love and support like anyone else.

"As Christians we must be willing to present the truth about marriage, family and sexuality and to do so charitably and lovingly."

Ms Howell said she was not a Catholic, but her daughter Maddison had been baptised in the church and had chosen to attend Merici.

"I'm confident there would be a mix of Catholics who believe in same-sex marriage," Ms Howell said.

"Heterosexual people are the ones who are making babies... so of course Catholics are going to be producing gay children, it's not a choice."

Ms Howell said she complained to the school about the pamphlet and principal Loretta Wholley had been apologetic.

The school distributed the letter "under the directive of the Archbishop", Mrs Wholley said in a statement, as it was "under the trustee" of the church and archdiocese.

"It has not changed who Merici College is or how we work in the classroom or beyond," she said.

"We are and will continue to be an inclusive Catholic school that promotes Christian values and supports girls on their academic, spiritual and personal journey."

Mrs Wholley said the school wanted its students to be "informed citizens" researching all aspects and understanding all points of view, especially when making "important ethical decisions".

"We have been impressed that many of our students have done this over the past 24 hours," she said.

"They have been thoughtful and considered in their responses with each other, and through social media."

Archbishop Prowse said it was unsatisfactory for the same-sex marriage debate to be one-sided.

"While I understand [it] has an array of complexities surrounding it, our intention is for our students and their families and communities to be informed as much as possible," he said.