(a) Before the expiration of the periods prescribed in Sections 111.104, 111.201, and 111.202 of this code for the filing of a refund claim or for the assessment and collection of any tax imposed by this title, the comptroller and a taxpayer may agree in writing to the filing of a refund claim or to an assessment and collection after that time. The agreement must contain the reasons the comptroller and the taxpayer wish to extend the period. At any time before the expiration of the period agreed on, the refund may be made, the tax may be assessed and collected, or an action may be commenced in any court to collect the amount delinquent.
(b) The extended period agreed on under Subsection (a) of this section may be extended by subsequent agreements made before the expiration of the extended period. All subsequent agreements must set forth the reasons for extending the period.

(c) No single extension agreement may be for a period of more than 24 months from the expiration date of the period being extended.
(d) The period for filing a refund claim or for assessment and collection of a tax may be extended if:
(1) without an extension, there might occur a revenue loss to the state;
(2) either the taxpayer or the comptroller, despite good faith efforts, requires more time to prepare for or complete the audit;
(3) without an extension, circumstances beyond the control of either the comptroller or the taxpayer would make an audit by the comptroller impractical or burdensome for either party; or
(4) an issue of law involved in the audit is awaiting determination in either litigation or an administrative proceeding.
(e) If, during an extended period agreed on under Subsection (a) of this section, the comptroller finds that an amount of tax, penalty, or interest has been unlawfully or erroneously collected, the comptroller shall credit the amount against any other amount then due and payable by the taxpayer from whom the amount was collected. The remainder of the amount if any may be refunded to the taxpayer.