Can the IRS extend the 90-day deadline to petition Tax Court?

No. The 90-day period (150 days if the notice is addressed outside the United States) is set by federal statute and cannot be extended by the IRS, by agreement, or by any other action. Contacting the IRS, requesting additional documentation time, or working with the Taxpayer Advocate Service does not pause the 90-day clock. If you miss the deadline, the Tax Court cannot hear your case and the proposed tax becomes assessed and immediately collectible.

What is the difference between a CP2000 and a Notice of Deficiency?

A CP2000 is a proposed adjustment — it invites you to agree or disagree before any assessment is made. A Notice of Deficiency (CP3219A or CP3219N) is a statutory legal notice that comes after the IRS has completed its review. Unlike a CP2000, a Notice of Deficiency gives you the right to petition the U.S. Tax Court before the tax is assessed — without paying first. If you ignore a Notice of Deficiency, the tax is assessed automatically after 90 days.

Do I have to go to Tax Court if I receive a Notice of Deficiency?

No. You have three options: agree (sign Form 5564 and pay or arrange payment), continue working with the IRS to provide additional information during the 90-day period (this does not stop the clock), or petition the U.S. Tax Court if you disagree and want a pre-payment judicial review. You may also resolve the issue through IRS Appeals in the meantime, though that does not pause the 90-day deadline either.

What is a Notice of Deficiency (90-day letter)?