You have to pay additional money in the form of the penalty and the interest on the penalty.
Make a written request for abatement. The tax code gives you the right to request cancellation of any IRS penalty. Nearly every one of the more than 140 penalty provisions of the code contains what is called a good faith exception. It means that if you acted in good faith and based upon a reasonable cause for your actions and not out of a deliberate attempt to cheat, deceive or mislead the IRS, the penalty does not apply. The procedure for seeking cancellation of penalties is remarkably simple. It does not even require a special form.
To make a request for cancellation of penalties, simply respond in writing to the IRS service center that issued the notice. Address your letter to the Penalty Abatement Coordinator and clearly identify it as a "penalty Abatement Request." Then, in great detail, give the facts and circumstances of the case. Take care to set forth details allowing the reader to conclude that you acted in good faith and based upon a reasonable cause for your actions, and not out of a deliberate attempt to cheat. Be clear not vague. Give dates and names where appropriate.
To the extent possible, provide copies (not originals) of documents you rely upon to support your claim. For example, if you claim that an auto accident prevented the filing of your tax return on time, provide all the details of the accident, including hospital and physician reports, insurance claims, medical bills, etc., to buttress your request. Always send your correspondence to the IRS using certified mail with return receipt requested.