In recent weeks, several EU states, notably Germany, Hungary, Austria and Slovenia have reinforced their border controls in a bid to stem the flow of undocumented migrants, sparkling speculation that the European Union's borderless Schengen area might collapse.
"Today the whole concept of the Project European Union is at stake," Karl Kopp said.
He added that the introduction of border controls between Schengen countries was a fatal mistake, that seriously threatens the free movement for Europeans.
Over half a million refugees from North Africa and the Middle East have arrived in the European Union this year, fleeing violence and poverty in their home countries, according to the European Commission.
On Tuesday, a YouGov poll revealed that four in five German citizens have a favorable view of the reintroduction of certain border controls.