The Red International of Labor Unions (Russian: Красный интернационал профсоюзов, romanized: Krasnyi internatsional profsoyuzov, RILU), commonly known as the Profintern (Russian: Профинтерн), was an international body established by the Communist International (Comintern) with the aim of coordinating communist activities within trade unions. Formally established in 1921, the Profintern aimed to act as a counterweight to the influence of the so-called "Amsterdam International", the social-democratic International Federation of Trade Unions (founded in 1919), an organization which the Comintern branded as "class-collaborationist" and as an impediment to revolution. After entering a period of decline in the middle 1930s, the Profintern was finally dissolved in 1937 with the advent of Comintern's "Popular Front" policy.

In July 1920, at the behest of Comintern head Grigory Zinoviev, the 2nd World Congress of the Communist International established a temporary International Trade Union Council, commonly known by its Russian acronym, Mezhsovprof. This organizing committee—including members of the Russian, Italian, British, Bulgarian, and French delegations to the Comintern Congress—was presented with the task of organizing "an international congress of Red trade unions.

Soviet trade union leader Solomon Lozovsky was named president of this new council, assisted by British unionist Tom Mann and Alfred Rosmer of France. The Executive Committee of the Communist International (ECCI) directed the new council to issue a manifesto to "all trade unions of the world", condemning the social democratic International Federation of Trade Unions based in Amsterdam as a "yellow" organization and inviting them to join a new revolutionary international union association.

This decision was to mark a split of the international trade union movement that followed the recently achieved split of the international socialist political movement into revolutionary Communist and electorally-oriented Socialist camps. This desire for a new exclusive international of explicitly "Red" union represented a fundamental contradiction with the Comintern's firm insistence that Communists should work within the structure of existing trade unions—an important detail noted at the time by delegate Jack Tanner of the British Shop Stewards Movement. Tanner's objection was brushed aside as Grigory Zinoviev denied him the floor, referring his complaints to committee.

Historian E. H. Carr argues that the decision to launch a Red International of Labor Unions at all was a byproduct of the era of heady revolutionary fervor that world revolution was around the corner, declaring:

"It was a step taken in a moment of hot-headed enthusiasm and the firm conviction of the imminence of the European revolution; and a device designed to bridge a short transition and prepare the way for the great consummation had unexpected and fatal consequences when the interim period dragged on into months and years."

As the plan for a new labor international moved forward, Mezhsovprof established propaganda bureaus in different countries in an attempt to win the existing unions affiliated to the rival "Amsterdam International," as the International Federation of Trade Unions was commonly known, over to the forthcoming "Red International." These bureaus attracted the most rebellious and dissident trade unionists to their banner while at the same time alienating sometimes conservative union leaderships, already raising charges that what was actually being proffered was dual unionism and a destructive split of the existing unions.

On January 9, 1921, ECCI decided that the launch of a new Red International of Trade Unions would take place at a conference to be convened on May Day of that year. An appeal was issued to the trade unions of the world who were "opposed to the Amsterdam International" and called for their affiliation to the new organization. This conclave was ultimately postponed until July, however, so that it could be synchronized with the scheduled 3rd World Congress of the Comintern—travel to and from Soviet Russia being a difficult and dangerous process in these years.