A hundred local community groups received an email from v on Friday saying the youth volunteering charity is taking on interim management of Millennium Volunteers on behalf of the Office of the Third Sector from 1 April.
Funding worth £15m has been allocated to the programme for 12 months, but so far money has been pledged only from 1 April to 31 December.
The announcement came after months of uncertainty and confusion, and it provoked criticism.
Sally Ellison, chief operating officer at Worcestershire Volunteer Centre, said: "All the uncertainty is putting young people off volunteering. It's very unsatisfactory."
Ben Silvey, manager of Young Bristol Action, a Millennium Volunteers provider, said: "Our contracts are getting progressively shorter. First they were for two years, then a year and now nine months. None of it seems to be particularly compliant with the ethos behind the Compact."
Mel Foster, communications director at v, said: "This is entirely consistent with previous announcements."