Article I, Section 1:
All legislative Powers herein granted shall be vested in a Congress of the United States, which shall consist of a Senate and House of Representatives.
No provision of the Constitution expressly authorizes either house of Congress to make investigations and exact testimony to the end that it may exercise its legislative functions effectively and advisedly. But such a power had been frequently exercised by the British Parliament and by the Assemblies of the American Colonies prior to the adoption of the Constitution. 1 It was asserted by the House of Representatives as early as 1792 when it appointed a committee to investigate the defeat of General St. Clair and his army by Native Americans in the Northwest and empowered it to
call for such persons, papers, and records, as may be necessary to assist their inquiries. 2
The Court has long since accorded its agreement with Congress that the investigatory power is so essential to the legislative function as to be implied from the general vesting of legislative power in Congress.
We are of the opinion, wrote Justice Van Devanter for a unanimous Court,
that the power of inquiry—with process to enforce it—is an essential and appropriate auxiliary to the legislative function. . . . A legislative body cannot legislate wisely or effectively in the absence of information respecting the conditions which the legislation is intended to affect or change; and where the legislative body does not itself possess the requisite information—which not infrequently is true—recourse must be had to others who possess it. Experience has taught that mere requests for such information often are unavailing, and also that information which is volunteered is not always accurate or complete; so some means of compulsion are essential to obtain what is needed. All this was true before and when the Constitution was framed and adopted. In that period the power of inquiry—with enforcing process—was regarded and employed as a necessary and appropriate attribute of the power to legislate—indeed, was treated as inhering in it. Thus there is ample warrant for thinking, as we do, that the constitutional provisions which commit the legislative function to the two houses are intended to include this attribute to the end that the function may be effectively exercised. 3
And, in a 1957 opinion generally hostile to the exercise of the investigatory power in the post-War years, Chief Justice Warren did not question the basic power.
The power of the Congress to conduct investigations is inherent in the legislative process. That power is broad. It encompasses inquiries concerning the administration of existing laws as well as proposed or possibly needed statutes. It includes surveys of defects in our social, economic or political system for the purpose of enabling the Congress to remedy them. It comprehends probes into departments of the Federal Government to expose corruption, inefficiency or waste. 4 Justice Harlan summarized the matter in 1959.
The power of inquiry has been employed by Congress throughout our history, over the whole range of the national interests concerning which Congress might legislate or decide upon due investigation not to legislate; it has similarly been utilized in determining what to appropriate from the national purse, or whether to appropriate. The scope of the power of inquiry, in short, is as penetrating and far-reaching as the potential power to enact and appropriate under the Constitution. 5
Broad as the power of inquiry is, it is not unlimited. The power of investigation may properly be employed only
in aid of the legislative function. 6 Its outermost boundaries are marked, then, by the outermost boundaries of the power to legislate. In principle, the Court is clear on the limitations, clear
that neither house of Congress possesses a ‘general power of making inquiry into the private affairs of the citizen’; that the power actually possessed is limited to inquiries relating to matters of which the particular house ‘has jurisdiction’ and in respect of which it rightfully may take other action; that if the inquiry relates to ‘a matter wherein relief or redress could be had only by a judicial proceeding’ it is not within the range of this power, but must be left to the courts, conformably to the constitutional separation of governmental powers; and that for the purpose of determining the essential character of the inquiry recourse must be had to the resolution or order under which it is made. 7
In practice, much of the litigated dispute has been about the reach of the power to inquire into the activities of private citizens; inquiry into the administration of laws and departmental corruption, while of substantial political consequence, has given rise to fewer judicial precedents.