"There was one individual who came along today, who I think the CWA could give a really good idea about what you're supposed to do with an egg," the prime minister told a Liberal event in the Victorian border town of Wodonga on Tuesday.

A woman wielding an egg had attacked from behind as he tried to leave an earlier meeting of the NSW branch of the CWA, known for its baking along with its community support and policy advocacy, in nearby Albury.

Mr Morrison was surrounded by older women eager to speak with him when the young woman wearing a maroon beanie made her way through the crowd.

She threw the egg which appeared to make contact with the back of his head before ricocheting off without breaking.

The woman was swiftly pushed to the ground by security personnel between a row of chairs.

A CWA member was also bowled over in the kerfuffle.

Outside, the egg thrower was spotted carrying a carton of six eggs. She refused to explain her motivation but mentioned Manus Island when pressed.

"I don't want to give a report, no thank you. I've got to go to work. No comment," she told reporters.

She had not meant for the other woman to be hurt.

"No, that was not my intention," she said. "I am sorry for that."

Inside, Mr Morrison put his arm around the older woman who had fallen over, as she found her feet.

"You're pretty tough!" he said as the pair shared a laugh before he moved off.

The 25-year-old woman is in police custody, pending further inquiries.

The prime minister tweeted soon after the incident.

"My concern about today's incident in Albury was for the older lady who was knocked off her feet," he wrote.

"I helped her up and gave her a hug. Our farmers have to put up with these same idiots who are invading their farms and their homes."

He expanded his attack to include unionists in a second tweet.

"We will stand up to thuggery whether it's these cowardly activists who have no respect for anyone, or militant unionists standing over small businesses and their employees on work sites."

ACTU secretary Sally McManus said the union movement did not condone such behaviour.

"How dare you accuse us of this & make the association. You seem to have no respect for the truth or any concern about running down your fellow Australians. We would never support such behaviour," she tweeted.

Independent Cathy McGowan is retiring from the regional Victorian seat of Indi, which takes in Wodonga, but her formidable campaign team has rallied behind health researcher Helen Haines.

Liberal Wangaratta branch president Stephen Hill believes Mr Martin is still in with a chance.

"The groundswell for the support that he's had is very, very good," he told AAP.

Australian Associated Press