Texas Tax Code - TAX § 31.06. Medium of Payment

(a) Except as provided by Section 31.061, taxes are payable only as provided by this section.  A collector shall accept United States currency or a check or money order in payment of taxes and shall accept payment by credit card or electronic funds transfer.

(b) Acceptance by a collector of a check or money order or of payment by credit card constitutes payment of a tax as of the date of acceptance if the check, money order, or credit card invoice is duly paid or honored.  If the check, money order, or credit card invoice is not duly paid or honored, the collector shall deliver written notice of nonpayment to the person who attempted payment by check, money order, or credit card.  Until payment is made in full by cash or by a check, money order, or credit card that is duly paid or honored, the lien securing payment of the tax remains in effect, whether or not the person receives notice of nonpayment.

(c) If a tax is paid by credit card, the collector may collect a fee for processing the payment.  The collector shall set the fee in an amount that is reasonably related to the expense incurred by the collector or taxing unit in processing the payment by credit card, not to exceed five percent of the amount of taxes and any penalties or interest being paid.  The fee is in addition to the amount of taxes, penalties, or interest.

(d) If a check or money order accepted in payment of taxes or the invoice for a payment of taxes by credit card is not duly paid or honored, the amount of any charge against the taxing unit for processing the check, order, or credit card invoice is added to the amount of tax due in the same manner as penalties and interest are added for taxes that are delinquent.  The tax lien on the property also secures payment of the amount of the charge.