IRS Publication 1281 Backup Withholding on Missing and Incorrect Name/TINs
The B-Notice procedure: CP2100/CP2100A, the 15- and 30-business-day rules, first and second notices, sample letters, and the 24% rate.
IRS Publication 1586 Reasonable Cause Regulations and Requirements for Missing and Incorrect Name/TINs
The IRS's own explanation of the solicitation schedule and how reasonable-cause waivers are evaluated.
IRS Publication 2108A On-Line Taxpayer Identification Number Matching Program
Eligibility, enrollment, interactive and bulk limits, and the result codes 0–8.
IRS Publication 1220 Specifications for Electronic Filing of Forms 1097, 1098, 1099, 3921, 3922, 5498 and W-2G
File formats for FIRE and the list of Combined Federal/State Filing participants.
IRS Publication 515 Withholding of Tax on Nonresident Aliens and Foreign Entities
Chapter 3 withholding, W-8 documentation, sourcing and treaty rules, and 1042-S reporting.
General Instructions for Certain Information Returns Forms 1096, 1097, 1098, 1099, 3921, 3922, 5498 and W-2G
Due dates, e-file threshold, penalties, corrections, and the exempt-payee rules.
Form W-9 and instructions Request for Taxpayer Identification Number and Certification (Rev. March 2024)
The line-1 name rules, disregarded-entity treatment, exempt payee codes, and electronic-W-9 requirements.
Form 945 and instructions Annual Return of Withheld Federal Income Tax
Deposit rules and annual reporting for backup withholding.
Form 1042-S and instructions Foreign Person's U.S. Source Income Subject to Withholding
Income and exemption codes for reporting payments to foreign persons.
IRS information return penalties page Penalty amounts by year
The current per-return amounts for late, incorrect and intentionally disregarded returns, and how to respond to a notice.
Rev. Proc. 2024-40 2025 inflation adjustments
Section 6721/6722 penalty amounts and calendar-year maximums for returns required to be filed in 2026.
Rev. Proc. 2023-34 2024 inflation adjustments
Section 6721/6722 amounts and maximums for returns required to be filed in 2025.
IRC §3406 Backup withholding
The statute: triggers, the rate, and payer liability.
IRC §6721, §6722, §6724 Information-return penalties and the reasonable-cause waiver
The penalty statutes and the waiver standard.
Treas. Reg. §301.6724-1 Reasonable cause
The definition of "responsible manner" and the solicitation schedule for missing and incorrect TINs.
Treas. Reg. §301.6011-2 (T.D. 9972) Electronic filing of information returns
The 10-return aggregate e-file threshold.
Pub. L. 119-21 (2025) 1099 threshold changes
Raised the 1099-NEC/MISC threshold to $2,000 for payments after 2025 (indexed from 2027) and restored the 1099-K $20,000 / 200-transaction threshold.
31 CFR Part 501 OFAC Reporting, Procedures and Penalties Regulations
The 10-business-day reporting rules for blocked property and rejected transactions.
OFAC sanctions lists SDN and Consolidated Sanctions Lists
The lists themselves, with search and download.
SAM.gov Exclusions
Federal exclusion records for contracts and grants.
HHS-OIG LEIE List of Excluded Individuals/Entities
Healthcare exclusion list with monthly updates.
NPPES NPI Registry National Plan and Provider Enumeration System
NPI lookup for healthcare providers.
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