A man who squashed a lemon meringue pie into the face of Qantas Airways chief executive Alan Joyce in Australia said he was protesting against his advocacy for same-sex marriage.

Irish-born Mr Joyce, who is gay, was giving a speech to 500 people in a Perth hotel yesterday when Tony Overheu approached from behind, pressed the pie into his face and then fled.

Overheu, a 67-year-old Christian and former sheep farmer, released a statement accusing Qantas and other companies that support marriage equality of "corporate bullying aimed at social engineering".

He was charged with giving police a false name.

Mr Joyce, 50, accused Overheu of "bullying" corporate leaders in an effort to suppress their views.

Our family is outraged, my wife is down my throat, I didn't understand that I'd breached the state's criminal code and the police are dealing with it. Clearly I regret that.

"I have every intention to continue to be vocal on these social and community issues," Mr Joyce said.

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

Mr Joyce has been singled out for criticism by government ministers for joining 30 chief executives of high-profile Australian companies who wrote a letter to Prime Minister Malcolm Turnbull in March calling for Parliament to legalise same-sex marriage.

Man is detained by security after throwing a pie at Qantas CEO Alan Joyce during a speech at a business breakfast in Perth yesterday.

Immigration minister Peter Dutton, a gay marriage opponent, told the CEOs to "stick to their knitting" and keep out of the political debate.

Mr Joyce said he had overwhelming shareholder support for his public stance.

Earlier today, Overheu said he hid behind a screen at the back of a stage for several hours before Mr Joyce rose to give his speech to a business breakfast.

Overheu said he chose lemon meringue from a cake shop the night before because it "appeared to be the softest, least likely to do any injury". He later sent Mr Joyce an email apologising.

"Our family is outraged, my wife is down my throat, I didn't understand that I'd breached the state's criminal code and the police are dealing with it. Clearly I regret that," Overheu said.

Police said Overheu was charged with giving officers false details, and the investigation was continuing.

Mr Joyce confirmed the apology, but added: "I'm not sure there's any regret at the issue that has occurred."

"My intention is to send a message that this type of behaviour isn't acceptable and I have every intention of pressing charges," Mr Joyce said.

"Nobody should be... intimidated, nobody should be bullied, nobody should certainly have an incident like occurred yesterday to try to stop people having that freedom of speech."