Norwood, which works with people with learning disabilities, is considering reducing the salaries of some of its staff as part of a cost-cutting review designed to save £3m a year.
The charity said it needed to make savings because it expected to lose £4m - 20 per cent - of its annual statutory income and is consulting staff about the possibility of pay reductions.
A spokesman for the organisation, which employs 1,200 staff and supports 280 adults in residential facilities in London and south-east England, said the charity paid above-average salaries to its staff. It preferred to explore options that would not result in redundancies, although it could not rule out job losses.
A reduction in salaries would "bring Norwood into line with other social care providers", the spokesman said.
Additional money-saving measures being considered include more partnership working with local providers on daytime recreational activities, a recruitment freeze for vacant back-office posts and a reduction in the number of external suppliers in order to create economies of scale.
Bernie Myers, chair of Norwood, said local authorities were the main buyers of Norwood services and the charity was already feeling the impact of the cuts announced in the comprehensive spending review.
"Norwood must now either substantially reduce its fees, or face the prospect of our local authority purchasers going elsewhere to buy the services we have historically supplied," he said.
"Failure to respond to this economic reality would put our entire organisation, our services and the people that we support at risk. This is something we cannot allow to happen."
The results of the consultation will be announced in January 2011.