(MICHIGAN) – The Michigan Department of Treasury sent erroneous Notice of Adjustment letters to approximately 27,000 taxpayers after tax season, with notices dated between April 7 and April 28, 2026.

Treasury said the problem came from a recent system change tied to processing 2025 state tax returns. The error affected the letters themselves, not the underlying returns, taxpayer accounts, or actual refund amounts.

State officials told affected taxpayers they do not need to respond. Treasury is issuing corrected letters, and the mistaken notices stopped being sent around April 20, 2026, though some may still arrive by mail.

The notices told some recipients that their Michigan income tax refunds or credits had changed. In many cases, the letters suggested reduced refunds, denied refunds, or unapplied prepayments.

Some notices also cited debts such as unpaid taxes or child support as reasons for the adjustments. Treasury said those statements were incorrect in these cases and did not reflect actual issues with the taxpayer’s account.

The agency said taxpayer prepayments remain correctly recorded in Michigan Treasury eServices. No login problems were reported for taxpayers checking those records online.

The scope of the problem made it a statewide issue rather than a handful of isolated notices. Approximately 27,000 Michiganders received the letters during a three-week stretch in April, according to the information released about the incident.

The dates matter because the letters were tied to a defined window. Taxpayers who received a Notice of Adjustment dated between April 7 and April 28, 2026 may have received one of the erroneous notices generated during the system change.

Treasury linked the problem to technical difficulties in a new IT system, or to a recent system change, used to process 2025 state tax returns. The malfunction sat in the letter-generation process, not in the tax data itself.

That distinction separates the paperwork error from the money. Treasury said no issues exist with individual tax returns or with actual refund amounts, even when the mailed notice suggested otherwise.

Taxpayers who want to confirm their records can review prepayments in Michigan Treasury eServices. The state said those records remain accurate even when a mailed notice suggested a payment had not been applied.

If a taxpayer is unsure how to read the letter, a tax professional can review it before any step is taken. Business analyst Mark Lee was identified as one tax expert taxpayers could consult while checking whether a notice matched their filed return.

Recipients were also advised to forward a copy of the notice to their tax preparer for confirmation. Treasury said no amended return and no payment are needed in response to these erroneous letters.

Refund checks call for more caution. Taxpayers were advised not to cash potentially incorrect refund checks and to return them to the state if applicable.

Mail delays mean the issue may still appear current even though Treasury said the faulty notices stopped going out around April 20, 2026. A letter arriving after that date can still carry an earlier date within the affected range.

The agency said it is resolving the matter internally. Corrected letters are expected soon, and Treasury said no individual response is required from taxpayers who received the mistaken notices.

The episode landed after the annual filing season, when many households were watching closely for refunds and account updates. In that setting, an official Notice of Adjustment that mentions reduced refunds, denied refunds, child support, unpaid taxes, or unapplied prepayments can look like a direct change to a return even when the underlying account remains unchanged.

Michigan residents checking mail from the Michigan Department of Treasury are left with a narrow practical test: compare the notice date to the April 7 through April 28, 2026 window, review prepayments in Michigan Treasury eServices, and wait for the corrected letter the state said it is sending.