A state income tax is any form of tax for which, under a state statute, (1) collection is provided, either by imposing on employers the duty of withholding sums from the compensation of employees and making returns of such sums to the state or by granting to employers the authority to withhold sums from the compensation of employees if any employee voluntarily elects to have such sums withheld; and (2) the duty to withhold is imposed, or the authority to withhold is granted, with respect to the compensation of employees who are residents of such state.