" The following statutes have been upheld against contentions that they did not operate equally upon all members of the same class: an act levying a higher gross receipts tax upon wholesale dealers in petroleum products than upon wholesale dealers in other commodities, Texas Company v. Stephens, supra; an ordinance requiring payment of a permit fee amounting to two per cent of the gross receipts from vehicles transporting passengers for hire but not imposing a similar burden upon operators of vehicles transporting freight for hire, Reed v. City of Waco, Tex.Civ.App., 223 S.W.2d 247 (wr. ref.); a statute levying an occupation tax on anyone owning or operating a nine or ten pin alley that was not coin operated, Youle v. Calvert, Tex.Civ.App., 348 S.W.2d 534 (wr. ref. n.r.e.); a statute levying an occupation tax upon the owners, managers and exhibitors of coin operated machines of every kind but exempting pay telephones, gas meters, pay toilets and sanitary cup vending machines, Ex parte Day, 127 Tex.Crim. R., 76 S.W.2d 1060; a statute imposing an occupation tax on the operation of coin vending machines of every kind but exempting pay telephones and gas meters, Ex parte Walker, 121 Tex.Crim. 145, 52 S.W.2d 266; an order of the commissioners court levying an occupation tax on peddlers of patent medicine but not taxing merchants and druggists selling the same medicine in the same county, South v. State, 72 Tex.Crim. R., 162 S.W. 510. See also 1 Cooley on Taxation, 4th ed. 1924, ยง 353.
The tax imposed by section 28 is clearly not an ad valorem or income tax. Nor may it be classified as an occupation tax, which `is levied for the exercise of the privilege of carrying on a business.' Youle v. Calvert, 348 S.W.2d 534, 535 (Tex.Civ.App.-Austin 1961, writ ref'd n.r.e.); Brunk v. State, 6 S.W.2d 353 (Tex.Crim.App. 1927). See also Attorney General Opinion WW-204 (1957).