15-30-2606. Tolling of statute of limitations. The running of the statute of limitations provided for under 15-30-2605 must be suspended during any period that the federal statute of limitations for collection of federal income tax has been suspended by written agreement signed by the taxpayer or when the taxpayer has instituted an action that has the effect of suspending the running of the federal statute of limitations and for 1 additional year. If the taxpayer fails to file an amended Montana return as required by 15-30-2619, the statute of limitations does not apply until 3 years from the date the federal changes become final or the amended federal return was filed. If the taxpayer omits from gross income an amount properly includable as gross income and the amount is in excess of 25% of the amount of adjusted gross income stated in the return, the statute of limitations does not apply for 2 additional years from the time specified in 15-30-2605.