The union had previously been involved in a Supreme Court case regarding the use of strikebreakers in strikes (NLRB v. Mackay Radio & Telegraph Co., 304 U.S. 333 (1938)), which it had lost.

[4] The United States Congress enacted the National Labor Relations Act (NLRA) on June 27, 1935, and President Franklin D. Roosevelt signed it into law on July 5.

On October 29, 1947, Charles T. Douds, regional director of the National Labor Relations Board in New York City, barred the American Communications Association from appearing on an NLRB-supervised union organizing election (its very first action under the new Taft-Hartley anti-communist oath provisions).

[10] On June 29, 1948, the United States Court of Appeals for the Second Circuit held, in a 2-to-1 decision written by Judge Thomas Walter Swan, that Section 9(h) did not impermissibly impose on union members' First Amendment rights.

[9] Although the Court was due to hear oral argument on January 13, 1949, it delayed this in order to take on another case (United Steelworkers of America v. National Labor Relations Board) with almost identical issues.

Associate Justice Wiley Blount Rutledge, a staunch liberal and strong advocate for civil rights,[17] had died unexpectedly of a stroke on September 10, 1949, at the age of 55.

[18] His successor, 59-year-old Sherman Minton, a former Democratic Senator from Indiana and a judge on the United States Court of Appeals for the Seventh Circuit, was nominated as his replacement on September 16, 1949, but was not sworn in until October 12.

[23] In Part II, Vinson posed what a plurality of the court believed was the key question:[24] We are, therefore, neither free to treat § 9(h) as if it merely withdraws a privilege gratuitously granted by the Government, nor able to consider it a licensing statute prohibiting those persons who do not sign the affidavit from holding union office.

[25] Citing In re Summers, 325 U.S. 561 (1945); Clarke v. Deckebach, 274 U.S. 392 (1927); and Hirabayashi v. United States, 320 U.S. 81 (1943), among others, Vinson noted that the Constitution often permitted otherwise irrelevant beliefs, personal traits, or employment status to be infringed upon in certain, limited circumstances.

[27] Vinson rejected the attempt to apply the "clear and present danger" standard as a mechanical test:[28] This confusion suggests that the attempt to apply the term, "clear and present danger," as a mechanical test in every case touching First Amendment freedoms, without regard to the context of its application, mistakes the form in which an idea was cast for the substance of the idea.

The provisions of the Constitution, said Mr. Justice Holmes, "are not mathematical formulas having their essence in their form; they are organic living institutions transplanted from English soil.

Their significance is vital not formal; it is to be gathered not simply by taking the words and a dictionary, but by considering their origin and the line of their growth.Congress had not concluded in enacting the Taft-Hartley Act that expressing communist beliefs was a danger; rather, Congress had wished to eliminate impediments to interstate commerce.

The fact that the injury to interstate commerce would be an accomplished fact before any sanctions could be applied, the possibility that a large number of such strikes might be called at a time of external or internal crisis, and the practical difficulties which would be encountered in detecting illegal activities of this kind are factors which are persuasive that Congress should not be powerless to remove the threat, not limited to punishing the act.Part VI of the decision discussed whether the statute impermissibly targeted the Communist Party as the sole political party seeking the violent overthrow of the United States government.

[38] Subsequently, Vinson interpreted Section 9(h) narrowly as barring from union office those who actually advocated overthrow of the government and not those who (for example) believed it would happen without their assistance.

... courts and juries every day pass upon knowledge, belief and intent—the state of men's minds—having before them no more than evidence of their words and conduct, from which, in ordinary human experience, mental condition may be inferred.

To require oaths as to matters that open up such possibilities invades the inner life of men...[50]Frankfurter acknowledged, however, that only these parts of Section 9(h) were invalid, and he would have remanded the case back to the district court with instructions for the union officers to obey only those constitutionally sound provisions.

[54] Jackson agreed with the majority that the Act did not infringe free speech, but rather merely withdrew the protection of the NLRA from unions which exercised their transparent choice to elect Communists as leaders.

[57] Agreeing that the Bill of Rights was not a suicide pact (as the majority had pointed out), Jackson nonetheless concluded that Congress had narrower, just as effective means of preventing the violent overthrow of the government than attempting to regulate thought.

"[63] Furthermore, Black said, the majority's decision does not prevent the government from "barring Communists and their suspected sympathizers from election to political office, mere membership in unions, and, in fact, from getting or holding any jobs whereby they could earn a living.

That claim "springs from the assumption that individual mental freedom can be constitutionally abridged whenever any majority of this Court finds a satisfactory legislative reason.

Test oaths were imposed in 16th century England because Protestant rulers feared papal control of their Roman Catholic subjects, Black noted.

"[70] Citing De Jonge v. Oregon, 299 U.S. 353 (1937), Black noted that a unanimous Court had already struck down laws which banned citizens from attending Communist Party meetings.

[13][76] A year later, the Court relied heavily on Douds' oath-as-predictor-of-future-action rationale in upholding a local government loyalty test in Garner v. Board of Public Works, 341 U.S. 716 (1951).

"[82] And the majority's claim[83] that any flaws in its approach can be easily rectified by appealing to the Supreme Court was not only scoffed at by Justice Black[64] but has also been sharply criticized by legal scholars.

[91] Frankfurter and a majority of the Court believed that the framers of the Constitution were not concerned as much with unfairness as they were with specification of the offense, the legislative (rather than judicial) determination of guilt, and retribution for past acts.

[98] In 1965, in United States v. Brown, 381 U.S. 437 (1965), the Supreme Court essentially overturned Douds by holding that the Taft-Hartley Act's oath constituted a bill of attainder, but did not formally do so.

[99] Two years later, in United States v. Robel, 389 U.S. 258 (1967), the Court specifically declined to apply a balancing test to a law prohibiting members of the Communist Party from holding jobs in the defense industry.

[100] Although the law was based on the same rationale as Taft-Hartley (that membership in the Communist Party was a sure indication of future action), the Supreme Court said this was too heavy an infringement on the individual's First Amendment rights.

[100] Instead, the Court seemed to suggest a new, two-part test: Whether the governmental interests advanced are valid, and whether the statute is narrowly drawn to infringe on First Amendment rights in the most narrow way.

[100] The Court returned to the balancing test in Brandenberg v. Ohio, 395 U.S. 444 (1969), but this time concluded that prohibiting mere advocacy of violence was too heavy a burden on the First Amendment.