29 May 1937,
The Franco authorities of San Sebastian reported by circulating the ban on speaking in Basque and the filing of complaints. They created the Civil Guard with the guards who were in street clothes, to ensure that no one spoke of "language and dialector" that was not Spanish. The Franco regime strongly persecuted the Basque people, especially at the beginning, almost eliminating the language of public life. Fear of being denounced was imposed and language dropped considerably...
Source:
Xabier Irujo and Iñigo Urrutia, Juridical History of the Basque Language (1789-2023). (Ivap)