‘public policy’ and ‘public security’ must be interpreted strictly, so that their scope cannot be determined unilaterally by the Member States without being subject to control by the EU institutions (see, by analogy, judgment of 13 September 2016, Rendón Marín, C‑165/14, EU:C:2016:675, paragraph 82). 69 The Court has thus held that the concept of ‘public policy’ presupposes, in any event, the existence, in addition to the disturbance of the social order which any infringement of the law involves, of a genuine, present and sufficiently serious threat affecting one of the fundamental interests of society. As regards ‘public security’, it is apparent from the Court’s case-law that this concept covers both the internal security of a Member State and its external security and that, consequently, a threat to the functioning of institutions and essential public services and the survival of the population, as well as the risk of a serious disturbance to foreign relations or to peaceful coexistence of nations, or a risk to military interests, may affect public security (judgment of 13 September 2016, Rendón Marín, C‑165/14, EU:C:2016:675, paragraph 83 and the case-law cited). 70 In the present case, it should be noted that, in view of the nature and gravity of the two administrative offences referred to in paragraph 66 above and of the requirement that the concepts of ‘public policy’ and ‘public security’ be interpreted strictly, it does not appear that JY represents a genuine, present and sufficiently serious threat affecting one of the fundamental interests of society or a threat to public security in the Republic of Austria. It is true that those offences constitute an infringement of the provisions relating to the highway code undermining road safety. It is apparent, however, from both JY’s written observations and the Austrian Government’s reply to a question put by the Court at the hearing that those two administrative offences, which, incidentally, resulted in relatively low fines of EUR 112 and EUR 300 respectively, were not such as to lead to the withdrawal of JY’s driving licence and thus prohibit JY from driving a motor vehicle on the public highway. 71 Traffic offences, punishable by mere administrative fines, cannot be regarded as capable of demonstrating that the person responsible for those offences is a threat to public policy and public security which may justify the permanent loss of his or her status of citizen of the Union. That is all the more so since, in the present case, those offences resulted in minor administrative fines and did not deprive JY of the right to continue to drive a motor vehicle on the public highway. 72 It should be added, moreover, that should the referring court find that, in accordance with the assurance as to the grant of Austrian nationality, the latter has already been granted to the person concerned, such offences would not, in themselves, lead to withdrawal of naturalisation. 73 Thus, in the light of the significant consequences for JY’s situation, as regards, in particular, the normal development of her family and professional life, of the decision to revoke the assurance as to the grant of Austrian nationality, which has the effect of making the loss of the status of citizen of the Union permanent, that decision does not appear proportionate to the gravity of the offences committed by that person. 74 In the light of the foregoing considerations, the answer to the second question is that Article 20 TFEU must be interpreted as meaning that the competent national authorities and, as the case may be, the national courts of the host Member State are required to ascertain whether the decision to revoke the assurance as to the grant of the nationality of that Member State, which makes the loss of the status of citizen of the Union permanent for the person concerned, is compatible with the principle of proportionality in the light of the consequences it entails for that person’s situation. That requirement of compatibility with the principle of proportionality is not satisfied where such a decision is based on administrative traffic offences which, under the applicable provisions of national law, give rise to a mere pecuniary penalty. Costs 75 Since these proceedings are, for the parties to the main proceedings, a step in the action pending before the national court, the decision on costs is a matter for that court. Costs incurred in submitting observations to the Court, other than the costs of those parties, are not recoverable.