(b) Combined returns. The administrator may by regulation provide for the filing of one return which shall include the return required to be filed under this section, together with the employer's return required to be filed under any local law imposing a tax on earnings of nonresidents of the city adopted by the city pursuant to authority granted by the general city law.
(c) Deposit in trust for city. Whenever any employer fails to collect, truthfully account for, pay over the tax, or make returns of the tax as required in this section, the administrator may serve a notice requiring such employer to collect the taxes which become collectible after service of such notice, to deposit such taxes in a bank approved by the administrator, in a separate account, in trust for the city and payable to the administrator, and to keep the amount of such tax in such account until payment over to the administrator. Such notice shall remain in effect until a notice of cancellation is served by the administrator.