IRS Notice 10 states, "Changes to your [year] Form 1040 - Amount applied to [year] estimated tax: [$amount]". With Notice CP10 the IRS has proposed an adjustment to your return based on information they have obtained from third parties (Banks, Employers, Lenders, etc.), which indicate you owe more tax. This information is usually not wrong, but lacks proof to offset it. TaxHelpLaw will show you what documents you need to win! But you only have 60 days to respond.
Notice CP10 & Notice CP10T are used to deny an estimated tax payment into the next year while a Notice CP10A (see below) is used to adjust your Earned Income Credit. For businesses, the IRS uses Notice CP101.
This is not a bill and not an audit but is a math adjustment based on third party records. The IRS could audit you later. When you respond to the IRS be very careful what you say and what you send them. These will be used against you! Please follow the Prep Steps for IRS Notice CP10 and see Mr. Hopkins in Colorado Springs, Pueblo or Denver so an Action Plan can be prepared for your specific situation.
Various IRS Notices CP10: