Peter Bradon, head of research at Best Companies, said: "Charities are partly to blame, because too often they ask for money, not time. But CSR is not just about writing cheques."
Bradon made his comments last week at the announcement of the results of an annual accreditation scheme that rates companies on how well they treat their staff.
He added: "Forty per cent of our respondents did not know whether their organisation was making a positive difference to the world, and 60 per cent did not know whether their employers worked with local communities.
"The idea that you are involved in giving something back is probably the most important factor in determining levels of employee engagement."
Twenty not-for-profit organisations were among the 273 employers that made it on to the accreditation scheme, which ranked participants on a one to three-star basis according to how well they engage their staff.
Two voluntary organisations were awarded three-star status: the Sandwell Community Caring Trust, which last year was named by the The Sunday Times as the second best company to work for in Britain, and P3, the charity that targets homelessness and social exclusion.
A spokeswoman for Best Companies said: "The voluntary sector performed really well this year and came second only to recruitment companies."