Portugal: double taxation agreement, Article 15 Employments
(1) Subject to the provisions of Article 17, salaries, wages and other similar remuneration (other than remuneration to which Article 18 applies) derived by a resident of a Contracting State in respect of an employment shall be taxable only in that State unless the employment is exercised in the other Contracting State. If the employment is so exercised, such remuneration as is derived therefrom may be taxed in that other State.
(2) Notwithstanding the provisions of paragraph (1), remuneration derived by a resident of a Contracting State in respect of an employment exercised in the other Contracting State shall be taxable only in the first-mentioned State if:
(a) the recipient is present in the other State for a period or periods not exceeding in the aggregate 183 days in the fiscal year concerned, and
(b) the remuneration is paid by, or on behalf of, an employer who is not a resident of the other State, and
(c) the remuneration is not borne by a permanent establishment or a fixed base which the employer has in the other State.
(3) Notwithstanding the preceding provisions of this Article, remuneration in respect of an employment exercised aboard a ship or aircraft in international traffic may be taxed in the Contracting State in which the place of effective management of the enterprise is situated.