The IRS uses Notice CP518 to ask you to contact them immediately because your tax return is overdue. They usually only request tax returns if they think you owe. You might also receive a CP518 if you filed an extension but then later didn't file or if you had home mortgage interest but no income (the IRS wonders where you got the money).
Notice CP518B is sent to Businesses requesting that certain returns be filed. The problem businesses face is that the IRS penalties are so enormous that it is virtually impossible to extricate the business from the IRS grip.
Confusion about Notice CP518
You may believe that you did file but the IRS denies it. If you have the certified mailing receipt or overnight mailing label then you can argue about the filing date and there is a procedure for this. But, unless you have this evidence, it is usually better to just re-file than argue. However, since you are filing an original return you have the opportunity to gather your records and find more deductions!
Some of the tax years may not require returns. If returns are due they must be constructed and prepared with all advantage to you - the truth is the goal. Many people have lost some or all of their documents. We are masters at finding lost evidence from old records. See Lost Documents.
This IRS action is NOT an audit & you probably won't be audited. The IRS simply wants the returns. But, since they think you owe you must be careful, not rash.
Because of the procedural and legal issues, it is not always wise to rush & file a return. We need to get the IRS file and create an Action Plan for your specific situation. Before you contact the IRS or file returns, please follow the Prep Steps for IRS Notice CP 518 and see Mr. Hopkins!