A Sydney Baptist Church pastor has spoken out against an anti-gay marriage letter that was read to some Christian parishioners on Sunday morning.

The heads of the Catholic, Anglican and Greek Orthodox churches addressed Sydney church goers, reading a letter to parishioners in a coordinated campaign ahead of further parliamentary discussion on the issue this week.

But Pastor Mike Hercock from the Surry Hills Baptist Church says it is simply fear-mongering.

He says Christians should be able to make decisions for themselves.

"Of the various churches that will have that statement read out in their pulpits from Baptist churches, Anglicans and Catholic, how many of them will have an opportunity to respond to an alternative perspective?" he said.

"It will be clergy down. And yet we know that Christians have the ability to make their minds up for themselves."

The head of the Greek Orthodox Church has written to his congregation saying that altering the traditional form of marriage is, in his view, against the sacredness of marriage and of the family as taught by the Christian faith.

Sydney's Anglican Archbishop Peter Jensen says the campaign is about defending the institution of marriage for all.

"It's one of the fundamentals of the whole of our civilisation and any change to the legislation about marriage is going to impact everybody," he said.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 3 minutes 50 seconds 3 m 50 s Peter Jensen talks to AM Download 1.8 MB

Archbishop Jensen told the ABC he decided to act after the Catholic Church told him it would be circulating anti-gay marriage material on Sunday.

'Blatant scaremongering'

The Greens say parishioners who hear views from the pulpit about gay marriage are being misled.

The Greens on Sunday launched their own video campaign, calling on Prime Minister Julia Gillard and Opposition Leader Tony Abbott to step away from the debate and allow a free vote.

Greens Senator Sarah Hanson-Young says the message being presented to church goers is one-sided.

"It's sad that in churches this morning they are only going to be presented with one view," she said.

"Frankly it's scaremongering at its most blatant.

"The legislation before parliament will not force church groups to marry anybody they don't want to. The legislation is about removing discrimination in the Marriage Act."

Senator Hanson-Young says Ms Gillard and Mr Abbott are out of step with the majority of people and other world leaders and are simply "delaying the inevitable".

Reports into two separate bills by Greens MP Adam Bandt and Labor MP Stephen Jones will be tabled in the House of Representatives today.