Parents at a territory school have been called upon to lobby against the ACT government's marriage equality bill.
The Australian Christian Lobby (ACL) has begun its campaign against the bill, which was greeted with a standing ovation when it was presented to the Legislative Assembly on Thursday.
The vocal lobby has distributed a letter declaring Canberrans "should not acquiesce by remaining silent" and they should ask their MLAs to vote against or delay the bill.
The letter was sent to parents at Trinity Christian School this week in an email from principal Andrew Clayton, who wrote that the issue was "emotive" and parents should "respond according to your conscience".
"Although this is not a usual practice for me as principal, I believe it is an appropriate response given the potential this bill has to impact the very nature of our school," he wrote.
The letter was described by Australian Marriage Equality on Friday as ''scaremongering'' that would ''offend the many Christian supporters of reform''.
Calls to Trinity Christian School were not returned on Friday.
ACL managing director Lyle Shelton said the letter was sent to the lobby's Canberra database but he was aware it had since been circulated more widely, including by some schools.
The letter has angered some parents at Trinity Christian School who contacted Fairfax Media. One ''disgusted'' parent, who asked not to be named, said "I don't think it's appropriate at all".
The ACL letter said there had been no consultation with church leaders about the bill and it would be "naive to think" that any exemption for churches under the proposed legislation "will not be attacked in the future".
Attorney-General Simon Corbell said on Friday the bill allowed people to have their say.
Mr Corbell said claims of "a secret agenda" to remove exemptions for churches "are just wrong".
"Saying that it is doubtful that these would last … these are straw men being put up to try and argue against the reform,'' he said.
"I've actually been contacted by a number of people from different religious faiths who have sought to explicitly tell me that the Australian Christian Lobby does not speak for them and that there are many people of faith in our city who are supportive of extending equality to same sex couples.''
Mr Corbell said he had also been contacted by parents from Trinity Christian School in support of the reforms. "I'm not surprised but I am disappointed that the ACL continues to make a range of inaccurate claims about the bill that was presented this week," he said.
But Mr Shelton said the laws would erode freedom of religion and freedom of speech.
"In the very few jurisdictions overseas where this has happened there's been attacks on freedom of religion," he said.
He said Mr Corbell was trying to be "Nostradamus" by saying that would not happen in the ACT.
"Governments are free to represent their agendas but normally there would be a consultation process," he said.