There are thirty-one very special government employees mentioned in the 1987 Constitution's Article XI on Accountability of Public Officers as subject of Impeachment Proceedings.
15 Supreme Court Justices
7 Comelec Commissioners
3 Audit Commissioners
3 Civil Service Commissioners
The first thing to notice is that no Member of Congress (Senator, Congressman or Party List Rep) is listed as one of the Republic's impeachable "Constitutional Officers". It is for that reason that IMPEACHMENT is the SOLE and EXCLUSIVE power of the Congress, as the main political branch of the government. Impeachment is a political process, precisely because of this, but we should make no mistake that it is actually the largest and most important piece of the Judicial Power that is nonetheless invested entirely and compleatly in the Congress. It is a demonstration of the true meaning of Separation of Powers as clear as geological formation. For in the impeachment process one finds a completely separate JUDICIAL PROCEEDING that applies exclusively to the tenants of the above listed Constitutional offices, and to no one else among our population of 96 millions.
Notice that for ordinary citizens charged with a crime the process steps are:
1. A person is accused of a crime and charges are filed in Court to determine guilt or innocence.2. A trial is held at Regional Trial Court (RTC) in which one judge decides the outcome.3. The accused my appeal conviction at RTC to the Court of Appeals (CA). The RTC conviction may be affirmed by a vote of at least 3 judges out of 5 that must hear the appeal and review the case.4. If the CA upholds the RTC conviction, the accused may finally appeal to the Supreme Court (SCoRP) which will rule with finality. Only when a conviction is final and executory at this level is the person's initial presumption of innocence is completely overcome and sentence may be carried out consisting of fines and prison.
But in the case of IMPEACHABLE OFFICERS they cannot be processed in the manner described above without first being impeached and convicted of impeachable crimes. All cases of impeachment are processed solely and exclusively by the Congress as follows:
1. An impeachment complaint is filed in the House of Representatives which has the exclusive power to INITIATE a case of impeachment. If sustained by a vote of at least one third of the House Members, the case goes to the Senate for trial forthwith.
2. The Senate has the sole power to try and decide all cases of impeachment. If convicted the accused can only be removed from office and banned forever from holding any government office. In all cases of impeachment the Senate Impeachment Court is the Supreme Court whose decisions are final and executory and may not be review, reversed or modified in any way by the Supreme Court. Not even the Power of Executive Clemency can reverse the decision and sentence of the Senate Impeachment Court.
[Though of course, this was not strictly (or even laxly!) followed, as it was wantonly violated by Chief Justice Hilario Davide, but that's another old story.]
For reference here is Section 3 of Article XI:
Section 3. (1) The House of Representatives shall have the exclusive power to initiate all cases of impeachment.
(2) A verified complaint for impeachment may be filed by any Member of the House of Representatives or by any citizen upon a resolution or endorsement by any Member thereof, which shall be included in the Order of Business within ten session days, and referred to the proper Committee within three session days thereafter. The Committee, after hearing, and by a majority vote of all its Members, shall submit its report to the House within sixty session days from such referral, together with the corresponding resolution. The resolution shall be calendared for consideration by the House within ten session days from receipt thereof.
(3) A vote of at least one-third of all the Members of the House shall be necessary either to affirm a favorable resolution with the Articles of Impeachment of the Committee, or override its contrary resolution. The vote of each Member shall be recorded.
(4) In case the verified complaint or resolution of impeachment is filed by at least one-third of all the Members of the House, the same shall constitute the Articles of Impeachment, and trial by the Senate shall forthwith proceed.
(5) No impeachment proceedings shall be initiated against the same official more than once within a period of one year.
(6) The Senate shall have the sole power to try and decide all cases of impeachment. When sitting for that purpose, the Senators shall be on oath or affirmation. When the President of the Philippines is on trial, the Chief Justice of the Supreme Court shall preside, but shall not vote. No person shall be convicted without the concurrence of two-thirds of all the Members of the Senate.
(7) Judgment in cases of impeachment shall not extend further than removal from office and disqualification to hold any office under the Republic of the Philippines, but the party convicted shall nevertheless be liable and subject to prosecution, trial, and punishment, according to law.
(8) The Congress shall promulgate its rules on impeachment to effectively carry out the purpose of this section.