No legislator is allowed to hold office or positions in any government agency including government-owned or controlled corporations without forfeiting his seat in the Congress. Meaning, a member of the Congress is not prevented from accepting other government posts as long as he forfeits his seat as a legislator. What is not allowed is the simultaneous holding of a government office and the seat in the Congress. The purpose is to prevent owing loyalty to another branch of the government, to the detriment of the independence of the legislature and the doctrine of the separation of powers. Forfeiture of the seat is automatic. Thus for example, a congressman who was appointed as secretary of the Department of Budget and Management is deemed to have automatically forfeited his seat in the House of Representatives when he took his oath as secretary for DBM. No resolution is necessary to declare his legislative post as vacant.
Not every other office or employment is to be regarded as incompatible office. There are seats where it is permitted by the Constitution itself, eg. membership in the Electoral Tribunal and in the Judicial and Bar Council. Moreover, if it can be shown that the second office is actually an extension of the legislative position or is in aid of legislative duties, the holding thereof will not result in the loss of the legislator's seat in the Congress. Legislators who serve as treaty negotiators under the President..
No members of the Congress shall be appointed to any office in the government that has been crated or the emoluments thereof have been increased during his term. The purpose is to prevent public trafficking in public office. Some legislators who do not opt to run again in the public office might create or improve lucrative government positions and in combination with the President, arrange that they be appointed in those positions, all at the expense of public good.
The appointment however to the forbidden office is not allowed only during the term for which a certain legislator was elected, when such office was created or its emolument thereof. After such term, and even if the legislator is re-elected, the disqualification no longer applies and he may therefore be appointed to the office.