With the Schengen agreement temporarily suspended by several European countries, many MEPs are now worried as to whether it can continue to survive in its original 1995 form.
Named after a small town in Luxembourg, the treaty enshrines the free movement of people as a fundamental right of EU citizens. Although the original treaty was signed in 1985 by five countries, Schengen now incorporates 22 member states as well as four non-EU countries.
However, the recent terrorist attacks in Paris and an unprecedented influx of refugees have led a number of European countries to reintroduce border checks.
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From a business perspective, suspending Schengen could have a huge impact on the transport sector. As Latvian ECR transport committee member Roberts Zīle warns "It goes without saying that the migration crisis impact on Schengen will create enormous costs not only on both the transit of goods and on commuter routes."
Zīle gave the example of the Øresund bridge between Malmö in Sweden and Copenhagen in Denmark, where border controls "could change the behaviour of the labour force."
He also highlights the impact of restrictions on public finances. For several years, investment in cross-border travel has been an important part of EU transport policy. "If Schengen is deteriorating further, this is money down the drain."
German S&D transport committee member Ismail Ertug estimates that "going back to pre-Schengen times would add €10bn in costs to business every year in Germany alone."
Also, longer waiting periods for trucks, workers and goods at border crossings would mean, "consumers would have to wait longer and pay more for goods." Zīle points out that "border controls will surely leave an impact on the environment as well."
Finnish GUE MEP Merja Kyllönen highlights the impact of the refugee crisis on European shipping. "Merchant vessels have had a significant role in rescue operations in the Mediterranean both in terms of volume and activity - so significant in fact, that it is no longer sustainable."
The Finn believes member states are to blame for the current crisis. "When every member state is making their own decisions and acting on their own, the whole principle of freedom of movement and the functioning of the single market is under threat."
Barbara Kudrycka, Polish EPP Vice-Chair of the LIBE committee adds concerns over the tourist sector. "Dismantling the entire infrastructure of Schengen will be very costly and we cannot afford this expense."
Instead, Kudrycka calls on the EU to focus on "protecting external borders against illegal migrants by implementing a European border and coastal guard that can be created from Frontex and member states, collection and exchange of data between certain systems as well as an effective returns policy."
The Pole also complained about the lack of common actions and "solidarity". She dismissed ideas for a mini-Schengen by some member states as "dangerous" and leading to "further disintegration."
EPP Vice-Chair of the LIBE committee, Hungarian Kinga Gál agrees, saying, "without protecting the external borders of the Schengen area, it will be increasingly difficult to keep the internal borders open."
Dutch ALDE MEP Matthjis van Miltenburg, commenting on the problems at Calais, which has seen refugees regularly disrupting truck, ferry and train services says; "A situation with large numbers of refugees housed in 'jungles' like Calais is undesirable. It seriously affects the efficiency of our transport systems and leads to unnecessary safety risks. Besides the human tragedy, the economic damage is enormous."
According to Gál, this proves that "most migrants are not refugees in the classic sense, rather economic migrants with a clear aim of where they want to go."
Fellow LIBE member, UK ECR MEP Timothy Kirkhope, also warns that border controls are, "in no way the panacea that some people suggest."
He adds, "most European borders are hundreds of miles long. Erecting border checks at motorways will do little to stop people that have already made the journey from Syria going through a field." Kirkhope calls for a smarter approach focusing on putting resources into the external border and also "speeding up detention, processing and returns."
The British deputy also stresses the need for the EU and member states to follow current rules as set out by the Dublin process, meaning a person can only claim refuge in the first EU country where they arrive.
However, Kirkhope admitted that the "migration crisis" was not only affecting politics at an EU level but also "impacting on domestic politics right across the EU," with "the debate so polarised that the majority of people in the centre are overpowered."
Even although it is not a member of Schengen, the debate within the UK over continuing EU membership is increasingly shaped by the migrant crisis. "This goes as much for the UK and the referendum debate as anywhere else in the EU."
However, according to Polish MEP Kudrycka, the debates over the migration crisis and free movement of people has been conflated, turning British society, "not only against irregular migrants coming from third countries but also EU citizens who are in the UK benefiting from the EU right of freedom of movement."
She warns; "We have to remember that after leaving the EU, everyone will be losers; British society as well as the European community."
Despite the debate on migration, Italian EFDD LIBE committee member Ignazio Corrao still strongly believes in the free movement of people. "The redefinition of Schengen means questioning the identity of Europe."
For the Italian, "the EU and member states should deal with the problem jointly, with concrete actions rather than words."
Ultimately for Corrao, "the EU should show solidarity, rather than questioning one of the pillars of the EU. If the EU steps backs in relation to free movement of people, it will mean its end."