If you are referring to the penalty for the late filing of a sample letter to the IRS, there is typically no specific penalty for late filing of a letter to the IRS itself. However, if you are referring to the late filing of a tax return, which may require submitting the letter along with it, there are potential penalties involved. The penalty for filing a tax return late with the IRS depends on whether you owe taxes or you are due a refund. If you owe taxes and fail to file your return or request an extension by the filing deadline (usually April 15th), a late filing penalty is typically charged. As of 2021, the penalty is usually 5% of the unpaid tax amount for each month your return is late, up to a maximum penalty of 25% of the unpaid tax. If you are due a refund, there is no penalty for late filing, as the IRS does not penalize taxpayers for late filing when they are owed money. However, to claim your refund, you generally have a window of three years from the original due date to file your return. After that, the refund is typically lost. It is always advised to consult a tax professional or review the IRS guidelines for accurate and up-to-date information regarding penalties for late filing of tax returns.