Where the Law Is Being Broken
Modern asylum law is based on the conviction that every individual has a right to apply for international protection in case their life is threatened in their country of origin. Most national and international regulations concerning asylum are based on the 1951 Geneva Convention (Convention Relating to the Status of Refugees) , which, developed shortly after WW2, is still the most important international law act regulating refugees law. In line with the basic right to apply for asylum, the Geneva Convention includes the principle of non-refoulement (Art. 32, 33). Non-refoulement forbids states from returning anyone declaring the will of applying for asylum to a place in which they would be in likely danger of persecution. While there is no international legal definition of the term push-back, it can be understood as any behaviour violating the general rule of non-refoulement. Not allowing a person seeking protection the right to apply for asylum is generally an infringement of the Geneva Convention and as such should be considered a violation of international law. Collective expulsions of whole groups, as they are conducted by several EU member states, deny each individual in this group the right to apply for asylum and explain their specific and individual reasons.
The principle of non-refoulement has been introduced in article 33 of the Geneva Convention. However, it has also been adopted as part of legal acts regulating or referring to asylum on the European level. Since all legal acts on asylum that are adopted by the European Union have to be in accordance with international law, push-backs are illegal both from the perspective of international and European law. Examples of EU regulations can be found in Art. 18 and 19 of the Charter of Fundamental Rights of European Union  and in Directive 2013/32/EU of the European Parliament and of the Council  of 26 June 2013 on common procedures for granting and withdrawing international protection.
Thus, the obligation to comply with the international law and standards on refugee protection lies with all countries that signed up to the 1951 Geneva Convention – including all member states of the European Union . Since all of the latter have also signed up to EU principles and regulations on its common asylum system  and are members of the Council of Europe, their responsibility is a double one. It is the responsibility of all member states to ensure that their common principles are not ignored on the external borders of the European Union.
 The 1951 Geneva Convention and the 1967 protocol relating to the status of refugees http://www.unhcr.org/protect/PROTECTION/3b66c2aa10.pdf
 CHARTER OF FUNDAMENTAL RIGHTS OF THE EUROPEAN UNION http://www.europarl.europa.eu/charter/pdf/text_en.pdf
 Directive 2013/32/EU of the European Parliament and of the Council of 26 June 2013 on common procedures for granting and withdrawing international protection http://eur-lex.europa.eu/legal-content/en/ALL/?uri=celex%3A32013L0032
 Parties of the Geneva Convention https://en.wikipedia.org/wiki/Convention_Relating_to_the_Status_of_Refugees#/media/File:Refugeeconvention.PNG
 Common European Asylum System https://ec.europa.eu/home-affairs/what-we-do/policies/asylum_en