and remit taxes pursuant to section 103(a) who is engaged in a trade or business shall register as a seller with the sales tax administering authority administering the taxes imposed by this subtitle. (b) Affiliated Firms Affiliated firms shall be treated as 1 person for purposes of this section. Affiliated firms may elect, upon giving notice to the Secretary in a form prescribed by the Secretary, to treat separate firms as separate persons for purposes of this subtitle. (c) Designation of Tax Matters Person Every person registered pursuant to subsection (a) shall designate a tax matters person who shall be an individual whom the sales tax administering authority may contact regarding tax matters. Each person registered must provide notice of a change in the identity of the tax matters person within 30 days of said change. (d) Effect of Failure To Register Any person that is required to register and who fails to do so is prohibited from selling taxable property or services. The Secretary or a sales tax administering authority may bring an action seeking a temporary restraining order, an injunction, or such other order as may be appropriate to enforce this section. 503. Accounting (a) Cash Method To Be Used Generally Registered sellers and other persons shall report transactions using the cash method of accounting unless an election to use the accrual method of accounting is made pursuant to subsection (b). (b) Election To Use Accrual Method A person may elect with respect to a calender year to remit taxes and report transactions with respect to the month where a sale was invoiced and accrued. (c) Cross Reference See section 205 for rules relating to bad debts for sellers electing the accrual method. 504. Penalties (a) Failure To Register Each person who is required to register pursuant to section 502 but fails to do so prior to notification by the sales tax administering authority shall be liable for a penalty of $500. (b) Reckless or Willful Failure To Collect Tax (1) Civil penalty