The Institute of Fundraising has called for the implementation of the Fundraising Preference Service to be delayed while an assessment of what it would mean for charities is carried out.
In its response to a consultation on the service, which closes today, the membership body says that so far charities have only been asked how the scheme should work.
The IoF also reiterates concerns that the service should not include a "total reset" button, which would enable people to opt out from all charity communications.
It says the total reset button would result in people not donating to charities they would have been happy to support because they would not be directly asked.
The consultation response says that there should be a pause in the implementation of the FPS while a full assessment of the impact on charities is undertaken.
"Now that the working group has delivered a proposed model, it would be right to revisit the merits and need for the FPS and the function that it needs to perform to shape the final proposal," it says.
"Good consultation and proper assessment does not start with the solution and work backwards."
It goes on to say: "It is deeply worrying that a sector-wide policy has been seemingly decided and now moving towards implementation without any form of impact assessment.
"A full analysis should now happen to properly assess the benefits and value of the full reset button alongside the consequences it will inevitably have."
It points out that the regulatory context for charities has changed since the initial idea for the FPS was put forward last year and thought should be given to whether the aims of the scheme could be met more effectively through other steps.
The response suggests that a more proportionate approach to a total reset button would consist of a signposting service, a "safe haven" for vulnerable people and the ability for people to select individual charities from which they no longer wish to hear.
It suggests a phased approach to introducing the FPS should be considered to enable proper assessment of how it is working for the public and charities.