Christian organisations that poured millions of dollars into the "no" campaign called for religious tolerance and freedom of speech in the wake of Tuesday's historic postal survey, swiftly linking the debate to "radical" sex education in schools.

Australian Christian Lobby managing director Lyle Shelton described the result as disheartening but praised the campaign with four million Australians voting against the legalisation of same-sex marriage.

"While we are naturally disappointed in today's result, we accept and respect the decision of the Australian people," Mr Shelton said.

The prominent campaigner called on the "yes" campaign to respect the rights of people who voted "no" to same-sex couples being married, linking the result to the welfare of children and sex education in schools.

"We will now do what we can to guard against restrictions on freedom of speech and freedom of religion, to defend parents' rights, and to protect Australian kids from being exposed to radical LGBTIQ sex and gender education in the classrooms."

Christian organisation FamilyVoice Australia called on politicians to intervene and protect the right of "no" voters who they alleged had been vilified and abused in the overwrought debate.

"Australia's politicians have an important task ahead," national director Ashley Saunders said.

"If they decide to ignore both our heritage and our biological reality by redefining marriage, then they must also enact broad and rigorous protections for the large percentage of Australians with religious or conscientious objections to it."

Mr Shelton claimed people opposed to same-sex marriage had been mobilised by the political debate, warning the battle would take place in classrooms around the country.

"Those who seek to deceive parents or deny them information about what their kids learn in school will find themselves called to account by millions of Australian mums and dads who now know what is at stake.

"Those who seek to push these ideologies through our schools and institutions will not get away with it so easily."

Defeated "no" campaigners brought attention to attacks on churches defaced during the debate and the case of a Canberra woman who was fired from her job after voicing her opposition to same-sex marriage on Facebook.

"The 'yes' campaign has repeatedly promised that legalising same-sex marriage will not compromise freedom of conscience and religion. They must now deliver on this promise," Mr Shelton said.