Tex. Utilities Code § 122.202: PENALTY FOR FAILURE TO PAY TAX.

A person who is required to pay a tax imposed by this chapter and fails to pay the tax as required by Sections 122.101 and 122.103 shall pay:

(1) a penalty of five percent of the amount of the tax due and unpaid; and

(2) if the tax is not paid before the 31st day after the date the tax payment is initially required to be made, an additional penalty of five percent of the amount of the tax due and unpaid.

Acts 1997, 75th Leg., ch. 166, Sec. 1, eff. Sept. 1, 1997.