If you have a donor who missed the deadline due to a reasonable cause, they may ask the IRS to waive the 50% excise tax. The request for waiver may be included in a letter of explanation, which they attach to their tax return (Form 1040) along with their Form 5329. When requesting a waiver, do not pay the excess accumulation penalty up front. Instead, follow the instructions for requesting a waiver in the Instructions for Form 5329. If the IRS does not honor their waiver request, they will be notified.