Australia's peak body for architects has backed down on its opposition to a security fence around Parliament House, just weeks after its own petition against the controversial plan attracted nearly 4000 signatures.

In December, the Australian Institute of Architects said it was "deeply concerned" by a decision to build a fence along the building's sloping lawns, warning it would destroy the character, heritage and symbolism of the national Parliament.

But the group has backed down after its president, Ken Maher, and other representatives were invited to a confidential briefing with Department of Parliamentary Services secretary Robert Stefanic.

Speaker Tony Smith and Senate President Stephen Parry have refused to release information about the 2.6 metre steel fence, citing security concerns. Plans for the fences across the sloping lawns at the front of the building were rushed through Parliament as politicians prepared to leave Canberra for the Christmas break. The exact location, design and cost are yet to be made public.