Q: Context: The professional tax is a slab-amount based on the gross income of the professional and salaried and as well as the other states as may be decided employee's. It is deducted from salary of the employee every month. In case of a company, directors of a company, partnership's, individual partners, self-employed professional or owner's of any business undertaken in the state, it is to be submitted depending upon their gross turnover in the preceding year. In some cases, the payment of tax is fixed and is to be paid irrespective of turnover. For example in state of West Bengal, owner of a factory has to pay professional tax only if the preceding year turnover is greater than 5 lac rupees and in case of companies there is a mandatory payment of rupees 2,500 /-each year as professional tax irrespective of turnover. For west bengal professional tax slabs and rates on employee or otherwise click here.

Question: professional tax payable on net salary or gross salary? Let's give stream of consciousness first:
The relevant sentence in the passage is: The professional tax is a slab-amount based on the gross income of the professional and salaried and as well as the other states as may be decided employee's. Therefore, the final answer is gross income.