Report of amended federal income or income tax withholding return

(a) Any taxpayer who files a timely amended federal income tax return resulting in a change in federal income or federal alternative minimum taxable income, or any employer who files a timely amended federal income tax withholding return shall also file, on or before the date that is 90 days after the date of filing of such amended return, an amended Connecticut income tax return (Form CT-1040X, or Form CT-1041, CT-1065, CT-G, or CT-1120SI, as the case may be, with the appropriate box checked to indicate that an amended return is being filed, or Form CT-941X), but only if the amendment of the federal return increases or decreases a taxpayer or employer's Connecticut income tax liability. Such report may be required at any other time if the Commissioner deems it necessary. Payment of any additional Connecticut income tax that is shown to be due on the amended Connecticut income tax return, plus interest, shall accompany the return. An employer filing an amended federal income tax withholding return shall attach to the Form CT-941X a statement showing the amount of Connecticut income tax that was originally withheld and reported, the amount of Connecticut income tax that should have been withheld and reported, and the reason for the increase or decrease in the amount of Connecticut income tax required to be withheld and reported.