Australian Christian Lobby managing director Lyle Shelton has compared the LGBT rights movement with the Holocaust, saying the "cowardice and weakness" of Australia's politicians is causing "unthinkable things to happen" like those in Nazi Germany.
One of the peak Australian anti-marriage equality groups, the ACL is expected to be a leader in the "No" campaign in an upcoming plebiscite on the issue.
In a blog post about what Australia can learn from the dead, Shelton writes about German expatriate Fritz Stern, who fled Nazi Germany as a child and wrote about the regime extensively.
"When I read the following quote from The Economist's obituary of Stern, I saw parallels with today," Shelton wrote.
"Hitler's rise, [Stern] argued, owed less to the Austrian corporal's personality, his thuggish supporters and brutish ideas, than to his opponents' cowardice and the weakness of Germany's 'gatekeepers' - the guardians of its cultural and moral standards."
"The cowardice and weakness of Australia's 'gatekeepers' is causing unthinkable things to happen, just as unthinkable things happened in Germany in the 1930s," Shelton wrote.
He cited the LGBTI anti-bullying program Safe Schools Coalition and the movement for marriage equality as two things that ought to be pushed back against.
"I am not saying people who dissent to today's cultural and political orthodoxy are about to be arrested by thugs wearing jackboots," Shelton wrote.
"Although Archbishop Julian Porteous was recently before the Tasmanian Anti-Discrimination Commission for six months for the crime of spreading Christian teaching on marriage and family."
In the same post, Shelton denied he was comparing the gay community to Nazis, saying Australia faced bigger issues than "the rainbow political agenda".
Shelton took to Twitter to further deny that he made the comparison to the Holocaust.
I have not said changing the definition of marriage & "Safe Schools" are like the Holocaust. Here's what I did say. https://t.co/SdsF9QAndr
Peak lobby group Australian Marriage Equality issued a statement asking that people ensure they "respect the dignity" of LGBTI people.
"Words can inflict terrible harm sometimes and we would ask that people of all opinions remember that. The use of intemperate language can cause deep hurt among LGBTI people and their families," said national spokesperson Shirleene Robinson.
Prime minister Malcolm Turnbull has said the plebiscite on marriage equality is likely to take place by the end of this year.