The London Voluntary Service Council is running its second Big Squeeze survey to find out how charities in the capital are coping with the difficult economic climate.
Last year's survey by the voluntary sector network for London discovered an increased demand for services and general uncertainty about funding.
The latest study will track how charities are being affected by cuts in public spending.
Peter Lewis, chief executive of the LVSC, which celebrates its centenary this year, said: "Although the latest indications show that the UK economy is no longer in recession, the social challenges are expected to persist for years to come.
"The 2010 Big Squeeze survey will show us how charities are responding to the challenges and what they need in order to continue to deliver for Londoners."
London's voluntary sector includes 30,000 registered charities, 5,000 social enterprises and thousands of unregistered community groups. It makes up 7 per cent of the capital's workforce.
Organisations can take part by visiting www.lvsc.org.uk/bigsqueeze. The survey closes at the end of February and the results will be released in March.