Liberal Canning by-election candidate Andrew Hastie's comments on Labor's support of Australian soldiers are "offensive" and "unwise", Opposition Leader Bill Shorten says.

Former SAS Captain Andrew Hastie on Thursday said that when he served in the military overseas, he did not think the then-Labor government had the soldiers' backs.

He is reported today as saying Labor MPs were more interested in having their photos taken with the troops in Afghanistan than helping them win the war.

Mr Shorten, who is campaigning with Labor candidate Matt Keogh in Mandurah ahead of tomorrow's vote, said that was wrong.

"Frankly, I'm offended by those comments," Mr Shorten said.

"I'm offended not because a Liberal politician makes a criticism of the Labor Party, I guess that's to be expected.

"But there's been a great tradition in this country that Liberal and Labor, together support our defence forces.

"I think what we need to do is stop having this argument about who loves this country more.

"The political debate shouldn't be used as some sort of football where we see the ADF dragged into it. I really think they were very unwise comments."

Hastie also critical of Labor's 'force ratios'

Mr Hastie was also reportedly critical of Labor's 2012 decision to introduce "force ratios", requiring 50 per cent Afghan soldiers and 50 per cent Australian troops when going into action.

He was this morning asked to clarify the comments at a press conference in Armadale, in Perth's south-east, with Justice Minister Michael Keenan.

"People asked me yesterday why I went into politics and I've got first-hand experience of what it's like to serve inside a policy framework," Mr Hastie said.

"So the point I made yesterday was that the policy framework I worked under I didn't think was a great one and that's inspired me, among other things, to go into politics."

Mr Hastie was asked what he expected Labor veterans like state MPs Peter Tinley and Paul Papalia to make of his comments.

"They're entitled to their point of view, just as I am. And I was asked a question yesterday and I answered it honestly, and that's how I felt," he said.

Mr Hastie declined to offer more specific criticism.

Later, Deputy Liberal leader Julie Bishop campaigned in Mandurah alongside Mr Hastie and told reporters the previous Labor Government had cut the defence budget to the lowest level since 1938.

"What message did Labor think they were sending when they spent money on pink bats and cash-for-clunkers and overpriced school halls, when they were slashing the defence budget at a time of great volatility, both here and abroad?" Ms Bishop said.

Leadership debate

Mr Hastie and Labor candidate Matt Keogh both today also deflected suggestions the Liberal leadership change had assured Mr Hastie victory in tomorrow's vote.

Labor candidate for Canning, Matt Keogh, campaigning on solar power ahead of the by-election. ( AAP: Richard Wainwright )

Mr Hastie, who again focused his campaign rhetoric on local issues and reaffirmed his commitment to combating the drug ice, said he had spoken to new Prime Minister Malcolm Turnbull and had his support.

But he added he had paid little attention to the dramatic turnaround in the polls.

"I'm confident I've done everything I can to hear what the people of Canning have to say and win their support. And if I get over the line tomorrow, I'll be very humbled," he said.

Mr Keogh, who toured the Murdoch University health campus in Mandurah with Mr Shorten, said he was not concerned about a Galaxy Poll showing a 51-49 per cent lead after preferences to the Coalition nationally.

"Well, I think someone described Malcolm Turnbull taking over the Liberal Party as a bit of a sugar hit," he said.

"Most people know that sugar's actually not that good for you, and it seems like, based on the Galaxy poll that came out today, that they basically got the diet coke version of that sugar hit."

The by-election is being held following the death of sitting member Don Randall in July.

Mr Randall had built up an 11.8 per cent margin largely due to his personal popularity.