For some it's the symbol of gay and lesbian progress and the fight for equality, but for Liberal culture warrior Eric Abetz it's the flag of a hostile nation that has declared war on Australia.

Bureaucrats from the Department of Finance were baffled when the former minister used Senate estimates hearings on Tuesday to ask what protocols exist for the flying of flags inside government buildings.

He said a staff member of the department had reported that a rainbow flag, associated with the LGBTIQ community and the fight for same-sex marriage, had been displayed in the Finance foyer.

Senator Abetz told department officials and Finance Minister Mathias Cormann the flag's presence and political nature might upset some staff members. He proposed a group opposed to same-sex marriage should have similar rights.