Francisco Marcos (Tribunal de Defensa de la Competencia de la Comunidad de Madrid) has posted The Single National Market as a Constitutional Principle in Spain: Market Fragmentation through Autonomous Regions’ Rules and Decisions on SSRN. Here is the abstract:
When the 1978 Constitution opted for a market economy system as the principal mechanism for distributing goods and services it included other relevant declarations which seemed to imply that the Spanish market was to be a single one.
The principle of a single market is a Constitutional Court doctrine against a possible decentralization of government policies as this could lead to the national economic order fragmenting into various markets. This study analyses the implications to be drawn from this principle, assessing its efficacy as a brake on autonomous laws which distort business activity in the national market.
Note: Downloadable document is in Spanish.