Who raised the rainbow flag in Finance?

Veteran Liberal Eric Abetz has used a Senate hearing to nail down the flag protocol at the Department of Finance.

Senator Abetz on Tuesday revealed a member of the department had told him a rainbow flag was on display in its Canberra lobby.

That, he pointed out, was an activist flag used to promote the cause of legalising same-sex marriage.

"Some people support that cause, others don't," Senator Abetz said.

"If that is allowed, one imagines the Marriage Alliance banner should be flown equally."

Finance boss Rosemary Huxtable was not aware there was a flag protocol as such, neither was Finance Minister Mathias Cormann.

"No one has ever raised flag issues with me ... if there is any concern in relation to flags, it might be useful to that being raised," Senator Cormann quipped.