(1) Every S corporation that has Montana source income must file a form CLT-4S, Montana S Corporation and Composite Information Return, on or before the 15th day of the third month following the close of its annual accounting period.

(2) Approval of an extension to file the S corporation's federal income tax return for an S corporation automatically extends the time for filing the Montana return to the date approved for filing the federal return. A copy of the federal extension form must be attached to the Montana S corporation information return in order to receive the Montana extension.

(3) An S corporation required to file a Montana S corporation information return is subject to a late filing penalty if:

(a) the Montana S corporation information return is not filed by the due date (including extensions);

(b) a copy of the S corporation's federal return is not filed with the Montana S corporation information return; or

(c) a return is filed that does not include the following information:

(i) name, address, and social security or federal identification number of each shareholder;

(ii) the S corporation's Montana source income;

(iii) each shareholder's pro rata share of separately and nonseparately stated Montana source income, gain, loss, deduction, or credit, or item of income, gain, loss, deduction, or credit; and

(iv) each shareholder's pro rata share of separately and nonseparately stated income, gain, loss, deduction, or credit, or item of income, gain, loss, deduction, or credit from all sources.