15-31-506. Copy of federal return required -- report of amended federal return. Every corporation shall, upon request of the department of revenue, furnish a copy of its federal income tax return and the computation schedule filed for the taxable year or years that the department may specify in its request. If the amount of a corporation's taxable income reported on its federal income tax return or the computation schedule filed for a taxable year is changed or corrected by the United States internal revenue service or other competent authority, the corporation shall file an amended Montana return with the department within 90 days after receiving official notice of the change or correction. A corporation filing an amended federal income tax return changing or correcting its taxable income for a taxable year shall also file an amended Montana return with the department within 90 days after filing an amended federal income tax return.