The conservative US group that invited former Australian prime minister Tony Abbott to speak in New York says the event is not "intentionally secretive".
The Alliance Defending Freedom dinner will be held in New York later this week, but the organisation has not publicly announced the date and location.
The pro-Christian, Scottsdale, Arizona-based ADF opposes gay marriage, adoption by same-sex couples and abortion.
Mr Abbott arrived in Los Angeles on a Qantas flight on Tuesday (Wednesday morning AEDT).
"I don't know if it is intentionally secretive," ADF media relations director Bob Trent, discussing the event, told AAP on Tuesday.
"For us, it was never intended to be a public event.
"It was a dinner ADF was having and Tony Abbott aligned on some of these issues, and I think they thought he would be an interesting fella to hear from, so they invited him to come."
Mr Abbott is also reportedly scheduled to meet News Corp executive chairman Rupert Murdoch in New York.
The ADF is surprised by the media interest in their event.
"It is going to be in New York, we have invited variety of people," Mr Trent said, declining to detail who would attend.
"It's a private gathering and Tony Abbott will be there."
The ADF boasts on its website of having more than 3000 allied lawyers to help win court victories in the US and around the world.
It describes itself as "an alliance-building legal organisation that advocates for the right of people to freely live out their faith".
"Along with our work to defend human rights such as free speech and religious freedom, ADF affirms the good of marriage and the value of strong families around the world, particularly on behalf children, who flourish when society honours and promotes the roles of both mothers and fathers in children's lives," the ADF said in a statement sent to AAP.
"Mr Abbott has been a strong advocate for marriage and freedom throughout his career and has graciously agreed to address our private event."
Mr Abbott's sister, same-sex marriage campaigner Christine Forster, said his decision to address the group was "disappointing".
"It doesn't sit with my understanding of how he views the world, so, yes, I was surprised," she told Fairfax Media on Wednesday.
But she doesn't believe her brother is in any way winding back rights for the gay community, she said.
Meanwhile, Prime Minister Malcolm Turnbull defended Mr Abbott's right to speak at the function.
"He does have fairly a conservative position on issues like that, so he probably would find he's talking to people with similar views, perhaps," he told Network Ten on Tuesday.
"He is entitled to speak to such audiences as he wishes."
