Has the undyed diesel tax rate increased? Yes. Beginning July 1, 2017, the undyed diesel tax rate is increased to 21 cents. See important notice 17-08 for rate increases for subsequent years. May 10, 2017 19:23 Related articles Has the gas tax rate increased? Has the undyed diesel tax rate increased? Is compressed natural gas subject to sales and use tax? Which motor fuel tax forms are required to be filed electronically? When is computer software subject to the sales tax in Tennessee?