The Government has given charities a timetable for drawing up proposals to reform Gift Aid, payroll giving and share giving.
At the first meeting of the new Gift Aid forum, Ian Pearson, economic secretary to the Treasury, told sector umbrella bodies and officials that the proposals should be finalised by 30 September. The forum will meet every two months.
A spokesman for the Treasury said there was a "strong consensus" at the meeting that Gift Aid needed simplifying.
Umbrella bodies said they were pleased that the Treasury was developing a timetable for reform.
But Louise Richards, director of policy and campaigns at the Institute of Fundraising, said reform was taking too long.
"We're still concerned about the lack of progress," she said. "This most recent meeting was yet another talking shop, with no concrete movement made.
"There's an election coming up, and we don't know what effect that will have on what will actually get done."
Hannah Terrey, head of policy and public affairs at the Charities Aid Foundation, said that although reform was taking a long time it was important that any changes were made "in a systematic and detailed way" and that it could not be rushed.
She said the first forum had been a helpful step.
"It's a good idea to look at all tax-effective giving reliefs," she said. "This forum needs to be sure that improving Gift Aid does not harm other reliefs."
She said that the Treasury seemed more keen to simplify Gift Aid than to bring in wholesale changes to it, such as a composite rate or an opt-out mechanism.