Section 139Local Government Code of 1991 (Republic Act No. 7160), Sec. 139

Professional Tax. -

(a) The province may levy an annual professional tax on each person engaged in the exercise or practice of his profession requiring government examination at such amount and reasonable classification as the sangguniang panlalawigan may determine but shall in no case exceed Three hundred pesos (P300.00).

(b) Every person legally authorized to practice his profession shall pay the professional tax to the province where he practices his profession or where he maintains his principal office in case he practices his profession in several places: Provided, however, That such person who has paid the corresponding professional tax shall be entitled to practice his profession in any part of the Philippines without being subjected to any other national or local tax, license, or fee for the practice of such profession.

(c) Any individual or corporation employing a person subject to professional tax shall require payment by that person of the tax on his profession before employment and annually thereafter.

(d) The professional tax shall be payable annually, on or before the thirty-first (31st) day of January. Any person first beginning to practice a profession after the month of January must, however, pay the full tax before engaging therein. A line of profession does not become exempt even if conducted with some other profession for which the tax has been paid. Professionals exclusively employed in the government shall be exempt from the payment of this tax.

(e) Any person subject to the professional tax shall write in deeds, receipts, prescriptions, reports, books of account, plans and designs, surveys and maps, as the case may be, the number of the official receipt issued to him.