For the Senate of Spain, the alliance supported the aligned Agreement of the Catalans coalition, which was participated by both the PSC–C and the PSOE.

[1] The alliance was conceived within the Catalan parties' efforts at reorganizing the centre-left electoral space ahead of the 1977 Spanish general election.

[5] Contacts took place amid advancements from the PSC–R's "Left Front" of attracting the PSC–C into their alliance, a decision rejected by the latter on the grounds that its political project and that of the Front "absolutely diverged, in terms of motivations and goals".

[6] Speculation arose in mid-March that negotiations between both the PSOE and the PSC–C were well underway,[7] and on 29 March it was revealed that an agreement had been signed the previous day, under which both parties would advance towards their eventual merging into a single party.

It also provided for the eventual incorporation of the PSC–R ahead of a future unification of the entire Catalan socialist space,[8][9][10] but because of the agreement's permanent nature, several parties—such as the PSP, the PCC and other minor socialist groups—had been excluded from negotiations, at which these voiced their dissatisfaction by denouncing the "PSOE's hegemonic aspirations".