Labor leader Bill Shorten fears the "worst excesses" of America's far-right political movement could infect the Liberal Party.
Former prime minister Tony Abbott has agreed to speak this week at a function in New York run by the Alliance Defending Freedom.
The conservative Christian lobby group is seeking to influence opinion leaders within the United Nations to oppose homosexuality and abortion.
Opposition Leader Bill Shorten told reporters in Melbourne on Tuesday he was concerned about what it meant for the Liberal party.
"Some of those people have been associated with the worst excesses of the far religious right in America - everything from their trenchant and radical opposition to the right to choose, right through to people talking about criminalising homosexuality," Mr Shorten said.
"What Mr Abbott does is up to him but he's the former Liberal prime minister of Australia and what worries me is his views are commonly held within the right-wing of the Liberal party."
He said the Liberals now had a "presentable frontman" in Malcolm Turnbull.
"But the people pulling the strings - their views are identical to Tony Abbott's and that's not good for Australia's future," he said.
The organisation also has links to the Australian Christian Lobby.
Alliance Defending Freedom senior lawyer Roger Kiska addressed the ACL's 2014 conference in Canberra.
The same conference was addressed by Mr Shorten, fellow Labor MP Shayne Neumann and minister Michaelia Cash.
At that conference Mr Shorten stood up for same-sex marriage as being in line with the Christian values of compassion and respect.
Meanwhile, Mr Abbott's decision to recontest his Sydney seat of Warringah at the next election continues to reverberate.
Former Liberal president Shane Stone said Mr Abbott now had the responsibility to show he is a team player.
"He doesn't need to become Malcolm Turnbull's best mate, as that would be disingenuous, but he should be encouraged to send a very public message of support promoting the election of the Turnbull government," Mr Stone wrote in The Australian on Tuesday.
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