Prolonged economic difficulties are clearly a breeding ground for uncertainty and fear. The rise in Nationalism across Europe is a tangible symptom of such concerns. Protectionism would be another. This piece by Public Service Europe focuses on what it regards as an erosion of the fundamental EU right of the freedom of movement of persons.
It is not much of an extension to see how similar thinking leads to retraction and protectionism threatening anti-competitive pressures from across borders in national markets.