The International Labor Defense (ILD) (1925–1947) was a legal advocacy organization established in 1925 in the United States as the American section of the Comintern's International Red Aid network. The ILD defended Sacco and Vanzetti, was active in the anti-lynching, movements for civil rights, and prominently participated in the defense and legal appeals in the cause célèbre of the Scottsboro Boys in the early 1930s. Its work contributed to the appeal of the Communist Party among African Americans in the South. In addition to fundraising for defense and assisting in defense strategies, from January 1926 it published Labor Defender, a monthly illustrated magazine that achieved wide circulation. In 1946 the ILD was merged with the National Federation for Constitutional Liberties to form the Civil Rights Congress, which served as the new legal defense organization of the Communist Party USA. It intended to expand its appeal, especially to African Americans in the South. In several prominent cases in which blacks had been sentenced to death in the South, the CRC campaigned on behalf of black defendants. It had some conflict with former allies, such as the NAACP, and became increasingly isolated. Because of federal government pressure against organizations it considered subversive, such as the CRC, it became less useful in representing defendants in criminal justice cases. The CRC was dissolved in 1956. At the same time, in this period, black leaders were expanding the activities and reach of the Civil Rights Movement. In 1954, in a case managed by the NAACP, the US Supreme Court ruled in Brown v. Board of Education that segregation of public schools was unconstitutional.

Ever since the birth of the organized labor movement, economic disputes have been contested in the legal system. In some cases, an employer or government has gone to court to achieve termination of strike actions, or to seek prosecution for alleged malefactors for physical violence or property damage resulting from such turmoil. The use of the injunction by employers to prohibit specific actions and its enforcement by the courts occasionally resulted in groups of defendants being embroiled in the costly legal system for union activities. The Pullman Strike of 1894, which brought about the trial and imprisonment of the officers of the American Railway Union, is but one example.

The syndicalist Industrial Workers of the World was subject to particularly intense legal pressure, framed at times as "free speech" actions, and in other situations less ambiguously as legal actions against union organizers and activists for their economic activities. To defend its core activists and their activities from what was systematic legal attack, the IWW established a legal advocacy organization called the General Defense Committee (GDC). It raised funds and coordinated the union's legal defense efforts.

Government efforts to silence and jail conscientious objectors and anti-militarist political opponents of World War I in 1917 and 1918 resulted in more than 2,000 prosecutions. These cases led to the formation of a legal defense organization for these defendants called the Civil Liberties Bureau, continued today as the American Civil Liberties Union (ACLU).

The fledgling American Communist movement which emerged in the summer of 1919 quickly was subject to systemic legal attack as part of the First Red Scare. On November 7 and 8, 1919, New York state authorities, at the behest of the Lusk Committee of the New York state legislature, conducted coordinated raids upon headquarters and about 70 meeting places of the Communist Party of America (CPA).

This effort was expanded and intensified on the night of January 2/3, 1920 in a mass dragnet by the Bureau of Investigation of the Justice Department, coordinated by the newly appointed J. Edgar Hoover, 24-year-old assistant to the Attorney General of the United States, and remembered in history as the Palmer Raids. This followed a series of strikes and bombings in 1919, including one against US Attorney General Palmer. An estimated 10,000 arrests and detentions resulted from the latter operation, with hundreds held for possible deportation from the United States for alleged violation of immigration laws caused by their purported "anarchist" political activity.

There was a massive need for legal defense on the part of those arrested in connection with these official operations against the communist political movement. In 1920 the Communist Party established its first legal defense organization, the National Defense Committee (NDC), to raise funds and provide legal services for its adherents in legal trouble with criminal or immigration authorities. A number of leading communist activists, including political leaders Max Bedacht and L.E. Katterfeld of the Communist Labor Party (CLP) and C.E. Ruthenberg of the CPA, as well as attorney I.E. Ferguson, served on the governing Executive Committee of the NDC. CLP member Edgar Owens acted as Secretary-Treasurer. A number of prominent liberal and radical attorneys were employed by the group, including Swinburne Hale, Walter Nelles, Charles Recht, and Joseph R. Brodsky.

The NDC maintained headquarters in Chicago and coordinated its work with another radical legal defense organization based in the East called the Workers Defense Committee (WDC). The efforts of these groups to defend those arrested in the Palmer Raids was largely successful, with the result that ultimately fewer than 10% of those arrested in Hoover's January 1920 raids suffered deportation.