Volunteering England is set to shed 31 jobs - more than half of its workforce - because of cuts in government funding.
The charity has opened a 30-day consultation with staff and the trade union Unite on plans to reduce its headcount from 55 to 24 posts.
Volunteering England receives £1.6m of its £5.7m income from the Office for Civil Society’s strategic partners programme.
In August, the OCS said it planned to reduce the number of strategic partners from 42 to 15 and award a maximum of £500,000 to any organisation. It has yet to indicate which partners will be retained.
Justin Davis Smith, chief executive of Volunteering England, described the redundancies in a statement as "heartbreaking" and said it was extraordinary that it had to lose staff at a time of unprecedented interest in volunteering.
"We have to take these steps now to protect the future of Volunteering England against threatened cuts in funding," he said.
"It is extraordinary that we have to plan on cutting back our organisation at a time when there is more interest in volunteering than ever before.
"The coalition government’s big society is built upon volunteering, and Volunteering England has a crucial part to play in helping public and community services become more effective through involving volunteers."
Davis Smith urged the Cabinet Office, which houses the OCS, to consider a phased reduction of the strategic partners programme "so organisations such as Volunteering England can diversify our sources of funding".
A Volunteering England spokesman said it would not discuss which departments were likely to be affected by the cuts.
The job losses are part of a proposed strategy for 2011 to 2014 in which the charity will focus on improving policy and practice and engaging with the volunteering movement.
Volunteering England receives more than half its income from government sources, with £1.9m from the Department of Health, £525,000 from the soon-to-be-closed infrastructure quango Capacitybuilders and £500,000 from the Department for Work and Pensions.