Voluntary-sector umbrella bodies have thrown their weight behind the Charities Tax Reform Group's campaign on VAT.
The NCVO's director of public policy, Campbell Robb, said it was an issue members felt strongly about.
"Recent high-profile cases have shown that the Chancellor understands the considerable burden the current regime places on charities," he added.
"We are urging the Treasury to translate these one-off concessions into a comprehensive commitment to the voluntary and community sector."
Charities Aid Foundation also said it was "entirely supportive" of the campaign. Director of external affairs Simon Hebditch said CAF wanted to explore the issue of equality of treatment of VAT for different sectors.
"Private companies and the public sector have a different VAT regime to the voluntary sector," he said.
Acevo is also behind calls for reform. Chief executive Stephen Bubb said: "The UK's presidency of the EU is a good time to take a look at the issue, which has been unresolved for some time."