Spanish to English Tech/Engineering Construction / Civil Engineering civil works

"Estas actuaciones ordenadas por el Ayuntamiento de XXX, se llevan a cabo ejerciendo la acción subsidiaria; y durante los últimos 7 concursos cuatrienales, YYY ha venido siendo adjudicataria de una de las zonas de XXX.

This is from a construction company's track record. The activity is emergency demolition of condemned buildings, for example after a fire or explosion, or shoring when structural defects are detected. The 'acción subsidiaria' could mean that the company here acts as an arm of the City Council to all legal effects but I don't know if there is an equivalent term in English.