A state government granted licences to certain private operators to run stage carriages and contract carriages. The stage carriages could run only from one fixed point to another with fixed passengers without any right to pick up passengers en route. No such restrictions were imposed on contract carriages that were required to pay higher rates of tax than stage carriage operators. The contract carriage operators challenge the discriminatory nature of tax imposed on them. In respect of the above which one of the following is correct?