In 1909 then U.S. President and former Governor General of the Philippine Islands, William Howard Taft issued an Executive Order (reminiscent of PGMA's own infamous EO464) which prohibited all U.S. civil service employees from communicating directly with Congress without his permission:
President Taft: "It is hereby ordered that no bureau, office, or division chief, or subordinate in any department of the Government, and no officer of the Army or Navy or Marine Corps stationed in Washington, shall apply to either House of Congress, or to any committee of either House of Congress, or to any Member of Congress, for legislation, or for appropriations, or for congressional action of any kind, except with the consent and knowledge of the head of the department; nor shall any such person respond to any request for information from either House of Congress, or any committee of either House of Congress, or any Member of Congress, except through, or as authorized by, the head of his department."
But in 1912, the U.S. Congress responded with specific laws that bolstered the Congressional Power of Inquiry against such assertions of executive privilege with the 1912 Anti-Gag Law and Whistleblower Protection Laws (PDF) which mandated that "The right of any persons employed in the civil service . . . to petition Congress, or any Member thereof, or to furnish information to either House of Congress, or to any committee or member thereof, shall not be denied or interfered with.”
In the United States Congressional Oversight Manual it states that,
A traditional method of exercising the oversight function, an implied power, is through investigations and inquiries into executive branch operations. Legislators often seek to know how effectively and efficiently programs are working, how well agency officials are responding to legislative directives, and how the public perceives the programs. The investigatory method helps to ensure a more responsible bureaucracy, while supplying Congress with information needed to formulate new legislation.
Amazingly, just like the implied Power of Oversight of Congress, the Executive Privilege of the President is apparently also an implied power under the grander principle of the Separation of Powers in a tripartite government. Neither the US nor Philippine Constitutions even contains the term "executive privilege" --
EXECUTIVE PRIVILEGE: A Missing Clause in the US Constitution? Presidents have claimed the power to withhold information from the courts and Congress, but no clause of the Constitution speaks of such a power, and questions regarding this are contentious and undetermined. The Supreme Court has ruled that presidential communications are protected by a privilege that is "fundamental to the operation of government and inextricably rooted in the separation of powers under the Constitution."
Of course, the SCOTUS has decided many cases involving a conflict between Executive Privilege and the right of the Courts to that privileged information if it is evidence in criminal prosecutions of executive department officials, as happened in the celebrated 1974 case United States v. Nixon. However, although there are allegations of criminal wrongdoing in the ZTE NBN deal, the Senate Blue Ribbon Committee is clearly not a Court of law and there is no criminal proceeding there in which his testimony is required as evidence. This could be used to argue that US v. Nixon does not apply exactly to Neri v. Senate. But how DOES it apply, if it does at all?
Last year, during the hearings into cases filed against FG Mike Arroyo and resigned Comelec Chairman Benjamin Abalos, the Ombudsman panel decided to secure official transcripts of the various Senate hearings, thus taking judicial notice of those hearings, at which testimonies were after all rendered under oath. Clearly the Senate hearings have already gathered and produced information that potentially is material and relevant to a criminal proceeding. Indeed, it would not be the first time that an inquiry of the Congress has produced criminal prosecutions as well as evidence.
But U.S. v. Nixon was a case of conflict between the Executive and the Judiciary. The Supreme Court of the United States (SCOTUS) has never decided a case in which the Principle of Executive Privilege of the President is directly pitted against the Powers of Inquiry and Oversight of the Congress--which is precisely the awesome task that now faces the Philippine Supreme Court. in the coming landmark Supreme Court decision, ROMULO NERI v. SENATE of the PHILIPPINES.
There is one parallelism that is significant. Although in the United States the Power of Inquiry and Oversight into Executive branch operations is an implied power, in the 1987 Philippine Constitution it has the force of a full and uncontroverted Constitutional provision empowering not only House and Senate but their Committees:
1987 Article Six Section 21: The Senate or the House of Representatives or any of its respective committees may conduct inquiries in aid of legislation in accordance with its duly published rules of procedure. The rights of persons appearing in, or affected by, such inquiries shall be respected.
Moreover, it seems to me there is also basis for whistleblower laws in the related provision:
1987 Article Six Section 22: The heads of departments may, upon their own initiative, with the consent of the President, or upon the request of either House, as the rules of each House shall provide, appear before and be heard by such House on any matter pertaining to their departments. Written questions shall be submitted to the President of the Senate or the Speaker of the House of Representatives at least three days before their scheduled appearance. Interpellations shall not be limited to written questions, but may cover matters related thereto. When the security of the State or the public interest so requires and the President so states in writing, the appearance shall be conducted in executive session.
To make the English Compositional structure of the above provision clear, let me print it like this to make it clear why the Congress could easily pass a Whistleblower Protection Act,
"The heads of departments may,
 upon their own initiative,
 with the consent of the President, OR
 upon the request of either House,
as the rules of each House shall provide, appear before and be heard by such House on any matter pertaining to their departments."
In Senate v. Ermita and EO 464 above provision plays a central role, but not as the Constitutional basis for whistleblower protection as I am now suggesting.
In the scales of the Balance of Justice in the case of Romulo Neri are the implied power of Executive Privilege to withhold information from the Judiciary and Congress as against the enumerated power of inquiry of the Congress.
Continuing along this fundamentalist vein, intelligent Filipinos ought to be inquiring further now into the Constitutional basis of such power of inquiry, which does not exist for Executive Privilege except by implication.
There is a simple explanation why SCOTUS has never faced a case like Neri v. Senate. It is simply the historical fact that the US Presidents have steered clear of using executive privilege against the Congress. Part of the reason is that the US Constitution actually grants the Congress broad powers, explicit and implicit, to elicit information from all departments of the government in aid of legislation and oversight of administration--which is the entire process of making and remaking the laws.
1. The power of the purse.
2. The power to organize the executive branch.
3. The power to make all laws for “carrying into Execution” Congress’s own enumerated powers as well as those of the executive.
4. The power to confirm officers of the United States.
5. The power of investigation and inquiry.
6. Impeachment and removal. Impeachment provides Congress with a powerful, ultimate oversight tool to investigate alleged executive and judicial misbehavior, and to eliminate such misbehavior through the convictions and removal from office of the offending individuals.
For me, the overall picture that emerges is that the specific power of inquiry to conduct investigations in aid of legislation is part and parcel of almost anything the Congress does. Without the Power of Inquiry, the Congress cannot accomplish its duty to wisely make AND remake the laws.
The fulcrum issue for the Philippine Supreme Court's delicate balancing act in the forthcoming historic decision, Neri v. Senate, could be framed as follows:
If the Prayer of Romulo Neri to prohibit the Senate from arresting him for contempt is granted, how would it affect the ability of the Congress and the President to do their respective duties?
The power of inquiry is actually part of a large and interconnected set of powers all related to the Right of Congress to information to do its job of making and remaking all the laws of the land. This suggests to me that in fact, the Power of Inquiry IS the institutionalization of the Public's Right to Know. Press Freedom, which is the power of inquiry of organized commercial journalism, is also based on the Public's Right to Know. But in Congress, the Truth, the whole Truth and nothing but the Truth is required of all statements under oath or affirmation. That stringent requirement does not exist for the Free Press, which is allowed to sell not only the "truth" but also entertainment.
Thus, I would say that if the Supreme Court hold Press Freedom in the highest regard, it cannot but hold the Congress' Powers of Inquiry and Right to Information in aid of legislation to be at an even higher level of priority.
Finally, the vast enumerated powers of inquiry and oversight of the Congress represents the power of the entire Filipino people to know the truth so they can make and remake the laws for their own benefit and interest. This is to be balanced against the weight of Executive Privilege which belongs strictly speaking to exactly ONE PERSON only.