The Government is being urged by some MPs to abandon plans to fast-track immigrants applying for British citizenship if they volunteer.
The MPs fear the proposal would lead to the creation of bogus voluntary organisations that would charge immigrants for certificates saying they had volunteered.
Neil Gerrard, Labour MP for Walthamstow, told Third Sector he wanted the volunteering provision scrapped from the Borders, Citizenship and Immigration Bill, which received its second reading in the Lords last week and is expected to become law before Parliament's summer recess begins on 21 July.
"The cost of setting up a validation system to make sure the volunteering organisations are genuine would outweigh the benefits of the scheme," he said. "I will challenge the Government on this issue as the bill reaches its report stage during the next few weeks."
Liberal Democrat home affairs spokesman Tom Brake told Third Sector he was particularly concerned because of recent revelations that immigrants had claimed visas by using documents from fake colleges.
"This is a serious concern for the voluntary sector," he said. "I will put the minister for borders and immigration on the spot about this issue at the bill's committee stage."
Brake also urged the Government to give voluntary organisations more information about the proposals and help them to prepare ways of accommodating the new volunteers. He said there was a "huge degree of uncertainty" in the sector about the proposals.
Mike Locke, director of public affairs at Volunteering England, said he expected that the nationality checking service provided by local authorities would also be responsible for checking whether volunteering organisations were genuine. He said he was concerned the proposed system would put pressure on small organisations and create too much red tape.
A Border Agency spokesman said the Government would make it clear that volunteering done through fee-charging organisations would not count. He said active citizenship was central to its agenda and it was considering penalties for fraudulent referees.