Donations and donors signed up through payroll giving are falling into a "black hole", according to a charity that recently entered the payroll giving system.
Around a year ago the Charity for Civil Servants moved from its traditional methods of soliciting post-tax, regular giving from civil servants to working with payroll giving agencies in processing pre-tax donations.
The charity now estimates it is missing around £4,500 a month in donations.
As the charity signs up donors directly, forwarding on the forms to payment centres, it holds records of who has signed up, for how much, and when their donations are due to arrive.
Karen Grant-Bond, fundraising and individual giving manager at the Charity for Civil Servants, said: "We've got a really big problem where people seem to disappear.
"We've got a black hole where we're not receiving the money."
The charity's corporate fundraising officer Joseph Carroll said that delays between sign-up and the first donations of seven or eight months is not uncommon, but there are cases of having to wait 14 months to receive a gift.
"By adding a payroll giving agency to our process we seem to have increased the difficulties," he said.
Grant-Bond added that the problem was across all payroll giving agencies.
"Payroll giving is meant to be regular income for charities, but for us it's become a headache," she said.
"It baffles me that there is no transparency. We've been left in the lurch."
Speaking at the Institute of Fundraising's special interest group on payroll giving conference this morning, the institute's chief executive Peter Lewis expressed support for payroll giving, but reiterated the line: "We are calling for the whole system to be fundamentally changed to make it easier for people to give."