Catholics are being told that casting a "no" vote in the "vital" same-sex marriage postal survey will ensure the "health and future" of Australian society.
Melbourne Archbishop Denis Hart has written an open pastoral letter urging Catholics to vote in the Marriage Law Postal Survey, ensuring their viewpoint is heard "on this vital public issue".
The letter follows similar messages from the heads of the Perth and Adelaide archdioceses last week.
Archbishop Hart said it was important the church's "story" continued to be heard on important debates that shaped society, including marriage equality.
In reiterating the church's position that marriage was between a man and a woman, Archbishop Hart encouraged "all people of good will to embrace the fullness of that truth".
"We understand that ours is not the only viewpoint in our diverse society
"Many do not agree with it. Many people see this as an issue about ensuring equality for every and all relationships
"Yes, human rights are important. But so are human responsibilities. We are responsible for the impact of our decisions on future generations."
There are 5.2 million Roman Catholics in Australia, according to the 2016 Census.
While there was a "dignity" in being attracted to the same sex, Archbishop Hart said that respect for difference should be as important as a demand for equality.
"Things can be equal in all respects without having to be uniformly the same," he said.
Archbishop Hart recently told Fairfax Media that the church's 180,000 employees were expected to uphold its teachings "totally" if same-sex marriage was legalised and defiance would be treated "very seriously".
"I would be very emphatic that our schools, our parishes exist to teach a Catholic view of marriage," he said.
"Any words or actions which work contrary to that would be viewed very seriously.
In finishing his letter, Archbishop Hart called for Catholics to be active participants in the marriage debate but to ensure they were respectful when engaging in it.
In his pastoral letter, the Archbishop of Perth, Timothy Costello, said that the current definition of marriage was the best for families.
Archbishop Costelloe also said it was unfair for those arguing against marriage equality to be called homophobic or lacking in intellectual depth.
"It is cruel to claim that such people are devoid of love, compassion or understanding for those in same-sex relationships," he wrote.
Philip Wilson, the Archbishop of Adelaide, said the church believed "deeply in the holiness of marriage as part of God's divine plan for the human family".
He said Catholics should engage in the marriage debate with "grace, calm reverence and respect".
"There will be no place in this dialogue for criticism, abuse or denigration of other people or their individual choices," he said.
Sydney's Archbishop, Anthony Fisher, has not released a letter, however he did tell The Australian that legalising same-sex marriage would have broader consequences for religious freedom.
"In other parts of the world that have legalised same-sex marriage, those who believe in traditional marriage have been harassed or coerced into complying with the new view of marriage," he said.
"It would be extremely naive to think that won't happen here."
The postal survey will take place from next month when the Australian Bureau of Statistics begins mailing out forms.