The Archbishop of Glasgow has been urged to hand over a former college for priests to conservationists.
The building served as a college until 1980
Campaigners warned time was running out for St Peter's College in Cardross, Argyll and Bute, which has been eroded by weather and targeted by vandals.
In an open letter to Archbishop Mario Conti, The St Peter's Building Preservation Trust said the Grade A listed seminary was on its last legs.
The archbishop is yet to issue a response to the calls.
Last year the seminary was named as Scotland's most important modern building by architecture magazine Prospect.
The Catholic Church, which owns the building, has considered a number of plans for redevelopment but none has got off the ground.
Its latest application, involving a housing development, has just been rejected by Historic Scotland.
Now the preservation trust, set up 18 months ago, has called for immediate action.
The trust's letter states: "Repeated vandalism, in addition to rain damage, means the seminary is on its last legs.
"If nothing is done to the building this year, it will be lost to the nation.
"Since the trust was formed at the beginning of 2004, the expertise it has offered has been ignored and it has been forced to watch as the current estates department in the Church have brought this once beautiful building to its knees."
The trust wants the Archdiocese to give the site over to an organisation such as their own which will work to restore the building.
The college was designed by Glasgow architects Isi Metzstein and Andy MacMillan. It opened in 1966 and closed its doors 14 years later.