Volunteering England has warned that the Government's plans to fast-track the citizenship applications of migrants who do voluntary work make volunteering "close to compulsory".
The Borders, Immigration and Citizenship Act, which was passed in July, allows immigrants who have been in the UK for five years to gain citizenship within one further year, rather than three, if they can prove they have been an "active citizen" by volunteering.
Speaking at a policy discussion about the act, Mike Locke, director of public affairs at Volunteering England, said: "There is a surprising lack of knowledge within government about what the act is going to do. Before the act was passed, there was no real working out of what it would come to in practice."
The policy could distort the public's perception of volunteering, he said. "It's an awfully big incentive to volunteer and we're worried it may present a false picture of volunteering to the whole of our society. It's as close to compulsory volunteering as anything."
Tom Brake, the Liberal Democrat home affairs spokesman, who was on the House of Commons public bill committee for the act, said it was "a disaster waiting to happen".
"Volunteering shouldn't be used as a government tool in relation to immigration policy," he said. "A lot of acts are never implemented, and the Government could adopt this position."
Chris Hedges, a civil servant at the UK Border Agency, said the implementation of the act was "a work in progress".
"Our timing is rubbish," he admitted. "When we started this, volunteer and community groups were desperately seeking volunteers. But because of the recession there are more volunteers, and groups are not desperate for them any more."
The scheme is expected to be put in place by July 2011.