When the left-wing of the union movement split away, he remained loyal to the federation, and in 1923, he was elected to the executive of the General Confederation of Labour (CGT).
He joined the Economic and Trade Union Studies Committee, and publicly opposed the Labor Charter, an action which won him the Medal of the Resistance.
Immediately after the Liberation of France, the unions were reconstituted, and Capocci returned to his post as general secretary.
[1][2] Capocci remained opposed to the communist leadership of the CGT, and he was a leading activist in founding Workers' Force, as an alternative.
That year, he also won election as president of the International Federation of Commercial, Clerical, Professional and Technical Employees, serving until 1949, when he became vice-president.