Charities will be £300m a year worse off because of two major fiscal changes which came into force this week.
Advanced Corporation Tax Credit Relief finally came to an end after five years on 5 April.
The WM Company has estimated that the loss of the tax credit, axed by Chancellor Gordon Brown in his first budget, but mitigated by a tapered relief scheme, could cost the sector £110m a year.
The 10 per cent supplement on payroll giving also ended on 5 April. It has been estimated that this will make charities £200m a year poorer.
Richard Brumby, director of UK charitable funds at investment manager Credit Suisse, said: "What the Chancellor gives with one hand he takes away with the other - in fact considerably more so. He is pouring herbicide on the charitable flowerbed, but expecting flowers to bloom, and expecting plaudits for what he is doing."
He added: "Smaller charities up and down the country that rely on payroll giving are suffering."