Australian Defence Force members, including reservists, are banned from taking part in any political activities while in uniform.
The ADF says its policy is designed to ensure the armed forces remain apolitical.
The image shows Hastie in desert camouflage in Afghanistan in 2009 but also shows him holding newborn son Jonathan alongside his wife, Ruth, and is emblazoned with the slogan “not another politician”.
He has not taken down the image, which the troops he commanded had taken, from posters and billboards.
“It’s just a hint at, ‘Hey, for the past 13 years, I’ve been serving in uniform’ and my formative experiences as a leader were with the Australian Defence Force,” Hastie told 6PR radio on Thursday.
“I’m proud of that and I think it’s good to let taxpayers know that their money – a lot of it has gone into my professional development – has been well spent.”
Hastie said the ADF had “used a bit of policy to try and push me around, basically”.
“I had to decide whose authority I answered to. It was the people of Canning. As a federal parliamentarian, I don’t take orders from the military.”
Cabinet minister Mathias Cormann threw his support behind Hastie, saying his fellow West Australian had provided distinguished service as an SAS soldier.
“I strongly support Andrew Hastie’s decision to present himself to his constituents in this election, putting forward what is part of his life history,” he told reporters in Canberra.
The ADF recently said it had also asked Pat O’Neill, Labor’s candidate for the LNP-held seat of Brisbane, to remove images featuring him in army uniform from his political promotions.
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