(no objective justification on the facts): A child was born in Denmark to German nationals. They gave him a double-barrelled name. When they moved back to Germany, the German authorities refused to recognise a double barrelled name as it was not allowed under German law. Ps, the parents, challenged this on the grounds of incompatibility with articles 12 and 18. ECJ said that this was not discrimination/unequal treatment within article 12, but was a breach of article 18 freedom of movement on the basis that the child would be caused great difficulty in having different names registered in different places e.g. being treated as suspicious at customs.
ECJ: This infringement could be justified only if it was based on objective considerations and was proportionate to the legitimate aim pursued. ECJ accepted that objective aims might be the facilitation of determining a person's surname with certainty and continuity, to ensure that siblings have the same surname and to preserve relationships between members of an extended family. However these were not proportionate to the measure of a refusal by the competent authorities of a Member State to recognise the surname of a child as already determined and registered in another Member State in which that child was born and has been resident since birth.