What to do?...
Nonresident - Connecticut Tax Withheld in Error
If you were not a resident of Connecticut for any part of the year and you did not work in Connecticut at all during the year but Connecticut income tax was withheld by your employer or by a pension plan payer, you should attempt to have the employer or payer correct the error and issue you a corrected Form W-2 or 1099-R. If you cannot get a corrected W-2 or 1099-R, you must complete Form CT-1040NR/PY, the nonresident income tax form, for the year in which the tax was withheld and attach a copy of Form W-2 or other form showing Connecticut income tax withheld.
Completing the Return
If income tax was withheld from your pay or pension in error, you must file Form CT-1040NR/PY to request a refund. Complete Lines 1-5 following the directions on the form. Enter “0” on Line 6 if you had no income from Connecticut sources.
If you are filing a paper return, attach a statement to the front of the return explaining that you were not a resident for any part of the year and that you did not work in Connecticut during the year along with a copy of the W-2 Form showing $0 Connecticut wages and the amount of Connecticut tax withheld. If the W-2 from your employer shows Connecticut wages, then your employer must also issue to you a corrected W-2 showing $0 Connecticut wages, proving that you did not earn any of your income while working in Connecticut. (If you file electronically, retain this statement with your records. You may be required to provide this documentation after you file.)