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Your IRS Letter 673C, Explained
Also called: 673C, Duplicate Returns Filed Letter
Last reviewed 2026-07-12
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What this notice usually means
Letter 673C is titled Duplicate Returns Filed. It explains an adjustment or refund. The IRS sends it to a business account when it finds more than one employment tax return, such as Form 941, for the same tax period. This often happens when a business with several locations files a separate return for each location. It can also happen when the wrong tax year form or check box was used. The letter explains the adjustment or refund. It also tells you how to file correctly next time. The IRS decides how the account is adjusted.
See every source line for this notice
“Letter 673C, Duplicate Returns Filed; Adjustment or Refund Explained”
“If taxpayer filed separate returns (Form 941/943/944/945/CT-1) for multiple locations, send Letter 673C and advise taxpayer to file only one tax return per tax period (in the future), even though several businesses are involved.”
“Duplicate filing conditions are sometimes caused by the incorrect use of a tax form or check box.”
What to do now
- 1
Read the letter for the reason given
Letter 673C explains which duplicate filing issue applied to your account. It also says how the IRS fixed it.
- 2
File one return per tax period going forward
If your business has several locations, file just one return for the period. Do not file a separate return for each location.
- 3
Use the correct tax year form next time
If the duplicate filing happened because the wrong tax year form was used, use the correct year's form for future filings.
- 4
Mark the correct period and check box
If the issue was a wrong check box, make sure the correct tax period is clearly marked on future returns.
- 5
Call the number on your letter with questions
If your letter is unclear, call the number printed on it.
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Sources
- IRS, Internal Revenue Manual 3.13.222, BMF Entity Unpostable Correction Procedures (irs.gov)Retrieved 2026-07-12
- IRS, Internal Revenue Manual 21.7.9, BMF Duplicate Filing Conditions (irs.gov)Retrieved 2026-07-12
Last reviewed 2026-07-12
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