The motivations behind yesterday's bizarre pie attack on Qantas CEO Alan Joyce at a business breakfast in Perth have been revealed.

Former farmer Tony Overheu, who surprised the Dublin-born Joyce onstage by slamming a lemon meringue pie into his face, has spoken up, claiming that he wanted to make a statement about same-sex marriage.

The 67-year-old devout Christian said he was opposed to the pro-marriage equality stance Qantas has taken as Australia debates whether same-sex marriage should be legalised in the country:

"Alan Joyce is a very active individual in this process [towards marriage equality] and in that context he was appropriate [to target].

"I've never done that sort of thing, I'm a law-abiding person, but I think this is part of inevitable pushback.

"When the community is grumpy, figures who are overstepping the line have got to anticipate there will be pushback in some shape or form. The broad community have had a gutsful."

Overheu added that he had emailed Joyce and companies involved to "unreservedly" apologise for his behaviour:

"It was a very serious action to take and if it was going to be an effective statement, then it needed to be done in a manner that hit the target, in a sense, without causing any injury."

The Qantas boss, who is openly gay and spoke to Newstalk about his support for same-sex marriage last year (listen to the career and life-spanning interview below), has told reporters that he intends to press assault charges.

He said:

"The police are continuing their investigation and my intention is to send a message that this type of behaviour isn't acceptable and that I will have every intention of pressing charges.

"I have every intention to continue to be vocal on those social and community issues.

"It's important for our shareholders, our employees, and our customers. It's called good corporate social responsibility.

"I'm a big believer in the great Australian expression a fair government it's all about giving people equality."

He added that he did not believe Overheu was remorseful:

"I believe he sent me an email... and I believe there has been an apology coming in but I'm not sure there's any regret at the issue that has occurred."

Joyce was one of 20 leading chief executives in Australia to sign a join letter in support of marriage equality in March.

Speaking about Ireland's Marriage Equality referendum, he told Newstalk's Bobby Kerr in April 2016:

"It got great coverage in Australia and a lot of people were paying attention to it. And the civilised way in which the campaign was done here in Ireland... The way the debate occurred... I think the whole world looked at how Ireland has changed."

Joyce recalled how homosexuality was only recently decriminalised when he left Ireland in 1996.

"To see that change in 20 years to be the first country in the world to have it [same-sex marriage] in a referendum is absolutely phenomenal".