The Brazilian Workers' Confederation (Portuguese: Confederação Operária Brasileira, COB) was the first national trade union center in Brazil, founded in 1908, under the basis of agreement of the First Brazilian Workers' Congress of 1906. Through its newspaper, A Voz do Trabalhador, it allowed a certain coordination and exchange of information within the Brazilian worker movement at the national level. The COB was formed by national industry and craft federations, local and state unions, unions isolated in places where there were no federations and non-federated industries.

During the first years of existence, the COB brought together about 50 unions, especially those organized in the Workers' Federation of Rio de Janeiro (FORJ), in the Workers' Federation of São Paulo (FOSP) and the Workers' Federation of Rio Grande do Sul (FORGS), which were the main support bases of the Confederation, and also those organized in the Bahia Socialist Federation (FSB), in the Local Workers' Federation of Santos (FOLTS), among others.

COB members considered that it should defend the fundamental aspirations of the working class, without distinction of school or party, so that any member of an organization, whether they be social-democratic, socialist, anarchist or another tendency, could accept it entirely. It was considered that the condition for the success of the union was in its autonomy, which would guarantee the suppression of conflicts between the different political trends between the workers.

The first years of the 20th century gathered some conditions favorable to the outbreak of workers' demands in Brazil, with an economic environmental conjuncture to obtain gains, with a phase of expansion of the economy initiated in 1903 and the proliferation of workers' organizations focused on trade unionism. Most strikes in the early 1900s had a very circumscribed character, often limited to a single company. It was from 1903 that the movements began to involve entire sectors and sometimes several different sectors. The textile industry strike in the Federal District in August–September of that year was a milestone in this sense, especially for involving a sector submitted to mechanical work, with considerable presence of women and minors, and that did not have the organizational experience of skilled sectors, which were already organized into mutual associations. Another striking aspect of the strike was receiving the adhesion of other sectors, which gave it characteristics of a general strike, bringing together thousands of workers. The strike was preceded by a series of localized mobilizations that gave rise to the first industrial union of the Federal District, the federation of workers in tissue factories. The strike was harshly repressed and none of its demands were met. Despite the defeat, this movement launched the basis of a trade unionism based more in direct action in Rio de Janeiro. At the time, the stoppage was described as "the most important strike movement hitherto held in Brazil". A month after the strike the Federation of Class Associations was founded in the Federal District. Still in 1905 the Workers' Federation of São Paulo (FOSP) was founded. Both institutions illustrate the increase in the number of workers' associations and federations in the period that preceded the realization of first Brazilian worker Congress.

In December 1905, with the rise of the worker organizations, the Federation of Class Associations published in the Brazilian Associations Federation a convocation for the First Brazilian Workers' Congress, to be held in the Federal District in 1906. The call explained that "only Socialists take part in the Congress, the revolutionary elements are forbidden," since beside the intention to create the "General Union of Workers in Brazil, or any other that is chosen", it would be discussed "if the worker must or must not be political." The explicit repulsion to the revolutionary elements manifested tensions between the anarchist and socialist currents, which focused on the Brazilian labor movement at that time. In any case, the anarchists were still present at the Congress.

The Congress was held between April 15 and 22, 1906, in the Galego Center, in Rio de Janeiro, with the presence of 43 delegates representing 28 associations linked to industrial branches and sectores such as stevedores, rail and coffee workers, as well as those working in the service sector. Even if not being in the majority, the anarchists - among them Edgard Leuenroth, Joaquim Mota Assunção, Luiz Magrassi and Alfredo Vasques - managed to assert their theses, influencing the congress significantly. In this way, the approved resolutions reflected the influence of revolutionary syndicalism, the trade unionist conception advocated by Brazilian anarchists in that period. Thus, guidelines raised by anarchist militants including union neutrality, federalism, decentralization, direct action and the general strike, began to form part of the principles of the Congress' signatory unions. The choice of the revolutionary syndicalist option was informed by its ability to unify and the comprehensiveness of its program, which provided for the possibility of diverse political and religious opinions, prioritizing the field of economic struggle as the common interest of all workers, and was considered a victory for the anarchists, insofar as the pretensions of influential reformists of the Brazilian labor movement, as was the case of Pinto Machado, leader of the Workers' Union of Ingenuity, Rio de Janeiro. Congress also decided that a confederation and a union newspaper should be set up to provide assistance to federations and give voice to the collective associations. The objectives of this Confederation would be the promotion of the union of workers for the defense of their moral, material, economic and professional interests; straits of solidarity between the organized proletariat, giving greater strength and cohesion to their efforts; to study and propagate the means of emancipation of the proletariat and publicly defend the economic demands of the workers.

The Brazilian Workers' Confederation (Portuguese: Confederação Operária Brasileira, COB) began its activities in Rio de Janeiro in March 1908, two years after the first Brazilian Workers' Congress. According to its constitution, COB started to publish in Rio the journal A Voz do Trabalhador, whose first number appeared at the beginning of the year. During its first years of existence, COB united about 50 unions overall, with the main support bases of the Confederation being organized in the Workers' Federation of Rio de Janeiro (FORJ), in the Workers' Federation of São Paulo (FOSP), in the Workers' Federation of Rio Grande do Sul (FORGS) and in the Bahia Socialist Federation (FSB).

The first phase of the COB lasted until December 1909, when the twenty-first number of A Voz do Trabalhador came out, which then closed the doors. During this period, it presented news from the Confederation and the federated associations, of its meetings, assemblies and strikes; denounced exploitation and working conditions in factories and other workplaces; encouraged the fight for the eight-hour day, also organizing advertising rallies for this purpose. were also held rallies against the Adolfo Gordo Law and the expulsion of immigrants and against a possible war between Brazil and Argentina. COB also organized rallies protesting against the Spanish Government's execution of the anarchist pedagogue Francesc Ferrer. During the years 1910, 1911 and part of 1912, COB and the working federations did not have great performance.