The tax assessments are what result from the misreported income

additional tax liability

[dokonać przypisu]
to charge additional tax (liability) to the taxpayer's account
to post additional tax (liability) to the taxpayer's account

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Do Not Form 872 Consent To An Extension Of Time To Legally Charge Additional Tax.

Generally, the I.R.S. has three years from the filing of a tax return to charge additional tax, interest, and penalties (called the “Assessment Statute Expiration Date). Because many audits start around two years after a tax return is filed, and because I.R.S. audits tend to take several months, the I.R.S. auditor usually asks the taxpayer to execute I.R.S. form 872, Consent to Extend the Time to Assess Tax, including interest and penalties.
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A bullying I.R.S. auditor does not want you to know that an administrative summons is not a self-enforcing legal document, meaning that if a taxpayer does not comply with the administrative summons’ demands, the I.R.S. cannot do anything to the taxpayer: cannot arrest or jail, cannot charge a fine or penalty, and cannot charge additional tax liability.
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Many I.R.S. auditors brag, and act as though they have power to charge taxpayers additional tax liability. Such is nonsense! I.R.S. auditors have no power whatsoever to charge you any additional tax liability. In truth, I.R.S. can only charge additional tax liability in one of three ways: {1} you consent in writing to be charged additional tax liability, {2} I.R.S. proceeds to audit Notice of Deficiency and you fail to file an United States Tax Court petition within 90 days from the Notice of Deficiency date, or {3} the United States Tax Court determines additional liability by trial decision or by your settlement agreement.
http://www.ataxlawyer.com/irs-audit-representation/

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Note added at 5 hrs (2015-11-12 15:38:43 GMT)
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Notice of Deficiency (NOD)
Commonly called an “NOD” or “Stat Notice.” Generally, the final notice issued by the IRS. The notice includes the additional taxes due as the result of a notice, examination, or audit. The NOD also informs the taxpayer that without response the IRS will assess the additional taxes and turn the case over to the collections process.
http://www.taxaudit.com/glossary

Surtax
A tax levied on top of another tax. A surtax can be calculated as a percentage of a certain amount or it can be a flat dollar amount. A surtax is generally assessed to fund a specific government program, whereas regular income or sales taxes are used to fund a variety of programs. Thus, one unique feature of a surtax is that it allows taxpayers to more easily see how much money the government is collecting and spending for a particular program.

http://www.investopedia.com/terms/s/surtax.asp#ixzz3rKwWRfqm