CP2000 income mismatch
IRS flagged a difference between your return and what payers reported. Most resolve in the taxpayer's favor when properly disputed with documentation.
IRS — most common notice
CP3219A 90-day letter
Statutory Notice of Deficiency. You have exactly 90 days to file in Tax Court — after that, you lose the right to dispute without paying first.
26 USC §6212
Audit examination letter
Letter 525, 950, 915, 2202-B identify audit-related correspondence. Each has a different protest path through IRS Appeals.
IRM 4.10
EITC verification (CP75)
Refund held until you prove residency of qualifying children. Standard documentation: school records, medical records, lease.
IRC §32
Balance due (CP14, CP501, CP504)
Interest + 0.5%/month penalty accrue. CP504 = imminent levy. Installment agreements available online for balances under $50K.
IRC §6159
Claim disallowance
Letter 4364C / 105C denies your refund claim. 30 days to protest with Appeals, 2 years to file suit in district court or Court of Federal Claims.
IRC §7422