Originally, ILO membership was identical with League of Nations membership, since adherence to the League carried with it participation in the ILO. However, several countries that were not members of the League were admitted to the ILO, notably the US, which joined in 1934. In 1946, the ILO became the first specialized agency associated with the UN. The constitution of the ILO now provides that any nation that is a member of the UN can become a member of the ILO by unilaterally notifying the Director General that it accepts the obligations of the ILO constitution. Other nations may be admitted to ILO membership by a two-thirds vote of the International Labour Conference.
The ILO constitution originally made no provision for the expulsion of a member. However, two amendments adopted by the International Labour Conference in 1964 would have empowered the ILO membership, by a two-thirds vote, to expel or suspend any member that had been expelled or suspended by the UN or that had been found by the UN to be flagrantly and persistently pursuing by its legislation a policy of racial discrimination. The amendments were adopted in response to South Africa's policy of apartheid. These amendments never came into force for lack of ratifications. However, in 1972, the conference adopted another Instrument of Amendment about expulsions, which came into force on 1 November 1974.
A state may withdraw from the ILO by formal notification of its intent to do so, such withdrawal to be effective two years after the ILO receives the notification. Germany, one of the original members, withdrew in 1935. South Africa notified the organization of its intent to withdraw before the amendments that could have led to its expulsion were adopted. Its withdrawal became effective on 11 March 1966. South Africa rejoined the ILO on 26 May 1994. Albania withdrew in 1967. Vietnam withdrew in 1985, but rejoined in 1992. Fourteen other countries withdrew their membership at various times (11 of them during the World War II period), but all sooner or later rejoined the organization. The rules that govern original admission to membership also apply to readmission.
In November 1975, the US filed a two-year notice of intent to withdraw, stating at the same time that it did not desire or expect to leave the ILO but hoped to help the ILO "return to basic principles." US Secretary of State Henry Kissinger said that the ILO had been "falling back" in four fundamental areas: workers' and employers' groups in the ILO falling under the domination of governments; an "appallingly selective" concern for human rights; "disregard of due process" in condemning member states "which happen to be the political target of the moment"; and "increasing politicization of the organization." The notice of intent to withdraw was allowed to run its course, thereby ending US membership in the ILO in November 1977. On the return of the US to membership in February 1980, President Jimmy Carter said: "As a member of the ILO and with the support of other countries, the United States will seek to ensure that the ILO continues to serve the interests of the world's working men and women by promoting more and better jobs while protecting human rights and dignity."
As of June 2002, the ILO had 175 members.