The rules are part of the draft version of the institute's Code of Practice, Accountability and Transparency in Fundraising, which begins a three-month consultation period this week. Charities that sign up to the Fundraising Standards Board scheme will also have to comply.
Another key rule will require charities that offer beneficiary gifts, such as livestock for families in the developing world, to state "prominently" in their advertising and catalogues if such donations might be used for other purposes.
"This is one of the institute's most controversial codes to date," said Laura Thomas, policy and standards manager at the institute. "It makes sense not to claim that every penny in the pound goes to the cause, because it's rarely the case."
A spokeswoman for Comic Relief, which has been criticised in the past for promising every penny went to the cause, said: "We continue to be open on our communication of how donations are spent. Central to this is the Comic Relief promise that, for every pound received from the public, a pound goes to help people affected by poverty and social injustice."
Thomas said the Fundraising Standards Board would decide in the event of a complaint if a charity offering beneficiary gifts was communicating terms and conditions prominently enough.
- See News, page 4.