Before and after: Pictures from Reddit user angrydave show how his mate was asked to turn his Aboriginal flag singlet inside out. (Reddit)

Before and after: Pictures from Reddit user angrydave show how his mate was asked to turn his Aboriginal flag singlet inside out. (Reddit) Source: Reddit

Parliament House was the only place that took offence to the slogan on the man's Aboriginal flag singlet.

The Department of Parliamentary Services says it “regrets if any offence was taken” after security guards asked a man to turn his Aboriginal flag singlet inside out before entering the building.

Reddit user angrydave posted that he and a colleague tried to enter Parliament House earlier this week but immediately came under the scrutiny of parliamentary security.

Pictures posted on Reddit show a man wearing a singlet with the Aboriginal flag and the words 'White Australia has a black history' emblazoned across the front standing on Parliament’s forecourt.

Another picture shows the same man in the public gallery of the Senate chamber with the black singlet turned inside out.

“Protest paraphernalia including banners, placards and clothing with specific messages are not permitted into Parliament House,” a statement from the Department of Parliamentary Services says.

The Department says there is a wide spectrum of objects that can be used in protest.

"Protest paraphernalia can take many forms and therefore it is not possible to be totally prescriptive as to what is or is not acceptable,” it said.

“Security officers have exercised discretion in good faith and the Department of Parliamentary Services regrets if any offence was taken by the individual.”

Reddit user angrydave says he and his friend were testing the standards of buildings in Canberra’s Parliamentary Triangle.

“We were actually aiming to see how many government institutions we could get into in thongs,” he posted.

“The answer is all.”

The men say Parliament House was the only building to take exception to the singlet.

“Everywhere else we went that day (National Library, etc) didn't bat an eyelid.”