The letter from Stephen Bubb, chief executive of Acevo, and Kevin Curley, his Navca counterpart, insists that the agreement, which sets out how public and third sector organisations should treat each other, must be put on a statutory footing.
It cites "widespread cynicism" about the agreement's ability to improve relationships between the sectors.
"Public bodies either don't know about the Compact or they don't care, and in those situations we are left with not a leg to stand on," it says.
The question was no longer whether statutory powers were the answer, but what powers were needed, the pair told Third Sector.
A spokesman for the Office of the Third Sector said the Government was committed to looking at the issue.
An Acevo poll showed that 96 per cent of its members backed statutory powers for the Compact (Third Sector Online, 20 May).
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