The so-called SHIELD Act, which has been introduced in both Houses of Congress, would amend the Espionage Act of 1917 to make it a crime for any person knowingly and willfully to disseminate, in any manner prejudicial to the safety or interest of the United States," any classified information... concerning the human intelligence activities of the United States or... concerning the identity of a classified source or informant" who is working with the intelligence community of the United States.

Although this Act may well be constitutional as applied to a government employee who unlawfully "leaks" such material to persons who are unauthorized to receive it, it is plainly unconstitutional as applied to other individuals or organizations who might publish or otherwise disseminate the information after it has been leaked. With respect to such other speakers, the Act violates the First Amendment unless, at the very least, it is expressly limited to situations in which the dissemination of the specific classified information at issue poses a clear and present danger of grave harm to the nation.

The clear and present danger standard, in varying forms, has been a central element of our First Amendment jurisprudence ever since Justice Oliver Wendell Holmes first enunciated it in his 1919 opinion in Schenk v. United States. In the 90 years since Schenck, the precise meaning of "clear and present danger" has evolved, but the principle that animates the standard was stated eloquently by Justice Louis D. Brandeis in his brilliant 1927 concurring opinion in Whitney v. California:

Those who won our independence... did not exalt order at the cost of liberty... [They understood that] only an emergency can justify repression. Such must be the rule if authority is to be reconciled with freedom. Such... is the command of the Constitution. It is, therefore, always open to... challenge a law abridging free speech . . . by showing that there was no emergency justifying it.

This principle is especially powerful in the context of government efforts to suppress speech concerning the activities of the government itself, for as James Madison observed, "A popular Government, without popular information, or the means of acquiring it, is but a Prologue to a Farce or a Tragedy; or perhaps both." As Madison warned, if citizens do not know what their own government is doing, then they are hardly in a position to question its judgments or to hold their elected representatives accountable. Government secrecy, although sometimes surely necessary, can also pose a direct threat to the very idea of self-governance.

Nonetheless, the First Amendment does not compel government transparency. It leaves the government extraordinary autonomy to protect its own secrets. It does not accord anyone the right to have the government disclose information about its actions or policies and it cedes to the government considerable authority to restrict the speech of its own employees. What it does not do, however, is leave the government free to suppress the free speech of others when it has failed itself to keep its own secrets. At that point, the First Amendment kicks in with full force, and, as Brandeis explained, only an emergency can justify suppression.

We might think of this like the attorney-client privilege. The client is free to keep matters secret by disclosing them to no one. He is also free to disclose certain matters to his attorney, who is under a legal obligation to respect the confidentiality of her client's disclosures. In this sense, the attorney is like the government employee. If the attorney violates the privilege by revealing the client's confidences to a reporter, the attorney can be punished, but the newspaper cannot constitutionally be punished for disseminating the information.

Now, some may wonder whether it makes sense to give the government so little authority to punish the dissemination of unlawfully leaked information. But there are very good reasons for insisting on a showing of clear and present danger before the government can punish speech in this context.

First, the mere fact that the dissemination of such information might, in the words of the proposed SHIELD Act, "in any manner prejudice the interests of the United States," does not in any way mean that that harm outweighs the benefit of publication. In many circumstances, such information may be extremely valuable to public understanding.

Second, a case-by-case balancing of harm against benefit would be unwieldy, unpredictable, and impracticable. Clear rules are essential in the realm of free speech, and that is one reason why we grant the government so much authority to restrict the speech of its own employees.

Third, the reasons why government officials want secrecy are many and varied. They range from the truly compelling to the patently illegitimate. Human nature being what it is, public officials who want secrecy for questionable reasons are often tempted to "justify" their demand for secrecy by putting forth exaggerated, and even disingenuous, justifications. The clear and present danger standard requires the government to clear a high bar to restrict speech, in part to avoid squabbles about the "real" government interest.

Fourth, as we have learned from our own history, there are great pressures that lead both government officials and the public to overstate the potential harm of publication in times of national anxiety. A strict clear and present danger standard serves as a barrier to protect us against this danger.

And finally, a central principle of the First Amendment is that the suppression of public speech must be the government's last rather than its first resort in addressing a potential problem. If there are other means by which government can prevent or reduce the danger, it must exhaust those other means before it can suppress the freedom of speech.

In the secrecy situation, the most obvious way for government to prevent the danger is by ensuring that information that must be kept secret is not leaked in the first place. Indeed, the Supreme Court made this very point quite clearly in its 2001 decision in Bartnicki v. Vopper, in which the Court held that when an individual receives information "from a source who has obtained it unlawfully," that individual may not be punished for publicly disseminating the information "absent a need of the highest order."

The Court explained that if "the sanctions that presently attach to [the underlying criminal act] do not provide sufficient deterrence," then "perhaps those sanctions should be made more severe," but "it would be quite remarkable to hold" that an individual can constitutionally can be punished merely for disseminating information because the government failed to "deter conduct by a non-law-abiding third party."

This may seem a disorderly situation, but the Court has come to a sound solution. If we grant the government too much power to punish those who disseminate information, then we risk too great a sacrifice of public deliberation; if we grant the government too little power to control confidentiality "at the source," then we risk too great a sacrifice of secrecy.

The solution is thus to reconcile the irreconcilable values of secrecy and accountability by guaranteeing both a strong authority of the government to prohibit leaks and an expansive right of others to disseminate information to the public.

The bottom line is this: The proposed SHIELD Act is plainly unconstitutional. At the very least, it must limit its prohibition to those circumstances in which the individual who publicly disseminates classified information knew that the dissemination would create a clear and present danger of grave harm to our nation or its people.

A version of this was published in the New York Times on January 4, 2011 under the title A Clear Danger to Free Speech.