The Prime Minister's office has defended the use of a Liberal Party banner during a campaign event at an RAAF base, which Labor says was an inappropriate use of the military.

Prime Minister Tony Abbott stood with South Australian Liberal leader Steven Marshall at a Defence base in Adelaide last week in front of the banner which featured the party logo and slogans.

Opposition defence spokesman Stephen Conroy asked Defence Minister David Johnston whether he was happy with the use of the banner on a Defence base.

"Who authorised the use of a South Australian Liberal Party banner as a backdrop at the RAAF base Edinburgh for a joint press conference held by the Prime Minister and the South Australian opposition Liberal leader Steven Marshall on Thursday, 13 March, just two days before the South Australian election?" he said.

Senator Johnston accused Labor of politicising Defence when in office but told the Parliament he "didn't know" the answer to Senator Conroy's question because he was overseas last week attending meetings in London.

"I happened to be away in the United Kingdom all of last week. I do not know the circumstances. I am not aware of the circumstances," the Minister said.

Senator Johnston said he would have thought Labor had more pressing concerns regarding Defence policy to raise with the Government than the use of banners.

Labor has called on the Government to authorise the military to take down party banners in future and prevent them being used again.

"Will the Minister commit to taking steps to ensure that party political banners like those used by the PM at RAAF Base Edinburgh are never used again on Defence Force bases?" Senator Conroy asked.

"Will the Minister inform the PM that use of party political banners on Defence Force bases is completely inappropriate?"

A spokeswoman for the Prime Minister has defended the media event.

"The Prime Minister held a short, distinctly separate press conference following the end of formal proceedings," the spokeswoman said.

"No military personnel took part nor were they invited to."

The ABC has sought a comment from the Defence Department.