Chief executives body Acevo, the Institute of Fundraising and umbrella body the NCVO are among the signatories of the letter, which was sent after a meeting with Treasury officials this month.
Stephen Bubb, chief executive of Acevo, said charities felt like they were "being led up the garden path" after two years of talks on issues such as simplifying the rules for higher-rate taxpayers and whether to switch from the current 'opt-in' system to an 'opt-out' mechanism. The latter would assume a donor is a taxpayer and would like Gift Aid to be claimed.
"A consultation was launched two years ago and since then we have had nothing but a series of meetings," said Bubb. "There is a feeling we have been given a complete runaround. A line needs to be drawn under this: either the Government will reform Gift Aid or it won't."
A Treasury spokesman said the 2007 Gift Aid consultation had led to measures, announced in last year's Budget, to simplify the scheme, and since then the Government had been considering further reforms.
"Gift Aid is a very successful scheme and any changes need to be very carefully thought through," he said. "That is why the Government commissioned research earlier this year to inform decisions on reform. Ministers will need to consider the findings before making any decisions."
Shadow charities minister Nick Hurd said: "I can understand why the sector is frustrated by the pace of government. We are looking at ideas to reduce the administrative burden on charities."