The High Court has asked the CJEU to rule on the question, as part of a case between the Gibraltar Betting and Gaming Association (GBGA) and HMRC.
The CJEU will begin a hearing on 4 October on whether Gibraltar has the status of a separate territory to the UK within the EU, so that the provision of services between the two should be treated as intra-EU trade under the Treaty on the Functioning of the European Union.
Alternatively, the High Court has asked whether Gibraltar should be treated as a third country or territory, outside the EU, or in some other way.
The Court has also asked whether national measures of taxation can constitute a restriction on the right to the free movement of services.
The GBGA represents a number of Gibraltar-based gambling operators that deliver remote gambling services to consumers in Great Britain. It launched an unsuccessful legal challenge against changes to the UK's remote gambling laws in 2014.
The Act came into force at the end of 2014.