A public-law entity created in 1940, the vertically-structured OSE was a core part of the project for frameworking the Economy and the State in Francoist Spain, following the trend of the new type of "harmonicist" and corporatist understanding of labour relations vouching for worker–employer collaboration developed in totalitarian regimes such as those of Nazi Germany and Fascist Italy in the first half of the 20th century.

[5] Previous unions, like the anarchist CNT and the socialist UGT, were outlawed and driven underground, and joining the OSE was mandatory for all employed citizens.

In reality, candidates for these elections had to be approved by Francoist Spain and all the process was heavily controlled, as fascism had a very interventionist policy towards the labour market: full employment for men, even at the expense of low wages or inflation, almost no right to work for married women and no unemployment benefits at all.

At the very end of the Francoist State, the sindicato vertical lost its always limited power and illegal trade unions gained force.

The banned Communist Party of Spain (PCE) considered that the "union" was heavily lopsided in favour of capital but was there to stay, and decided to infiltrate it with their candidates in order to achieve practical gains for the workers' conditions.