We are learning from Case Studies in Business Ethics by the late Rabbi Dr. Aaron Levine z"l professor of economics at Yeshiva University.
"Someone who retracts a verbal commitment is called untrustworthy and a Jewish court will admonish and publicly reprove the offender for this misconduct. Nevertheless, breaking a promise is permissible in certain circumstances. Consider the following scenario:
Person A verbally commits himself to confer B with a largess. Subsequently, A has second thoughts and wishes to retract. Provided A made his commitment in good faith, his subsequent retraction is not unethical. Given the consider expense involved, B presumably never relied on the promise and hence A's retraction should not have dashed B's expectations."
My question on this: does that apply to a pledge made to a charitable organization or a shul? As someone who works for a not for profit, I know that we budget for the future based on pledges made to us by donors. If they were to retract we would be in serious trouble.