The NCVO's Coalition for a Charities Act opposes plans, proposed by the Charity Commission, which would define whether a charity is of public benefit according to whether it has a 'social and economic impact'.
Amnesty International, the National Society for the Prevention of Cruelty to Children and the British Heart Foundation are all members of the coalition, which is lobbying MPs, key policy makers and the bill's Parliamentary Scrutiny Committee to reject what it calls 'an inappropriate definition' of charitable status.
National broadsheet social affairs and education sections are also being targeted, along with the charity sector press.
'For many charities, any economic impact is likely to be incidental to their work,' said NCVO chief executive Stuart Etherington.
The coalition is calling on the Charity Commission to explain its reasons for the proposal.
It plans to table an amendment to the bill as it goes through parliament if the definition is not changed before this stage.