It is stated in the Plan of Urgent Measures for Energy Saving and Efficiency 2011, a document presented on 4th March by the Spanish Ministry of Industry.
One if these measures is called “Obligatory energy certificate for non-residential buildings with more than 400 kW of installed power”. It consists in making energy certificates compulsory in large buildings of the tertiary sector, e.g. private or public office buildings. “400 kW of installed power” refers to thermal power (heating and cooling), not electric power. Buildings are classified into two categories: one for buldings with installed power between 400 and 1000 kW and another for buildings with more than 1000 kW. The document, however, does not state the purpose of this classification.
Energy certificates will be required to include a list of technically and economically feasible efficiency measures, although the implementation of these measures will be voluntary.
The Spanish administration plans to begin executing these certificates in its own buldings and implement efficiency improvements whenever possible through a specific program coordinated by IDAE.
The whole set of measures as written in the document should be enough to reduce Spanish oil imports by 5%.
More info: Plan of Urgent Measures for Energy Saving and Efficiency 2011. Economic Report (In Spanish)