According to the CJEU press release:

"In 2023, certain third-country nationals, who arrived by aeroplane at Brussels airport, submitted applications for international protection. The Belgian authorities refused their entry to the national territory and detained them in centres located inside that territory as part of the border procedures laid down by EU law. At the end of the period of four weeks stipulated for those procedures, the examination of the applications continued on the basis of a priority procedure.

However, the Belgian authorities decided to keep the applicants in detention in the same centres, citing a risk of absconding. The asylum applications were subsequently rejected.

In the course of legal actions brought against those decisions, the Belgian court asked the Court of Justice about the compatibility with EU law of legislation authorising a Member State to detain persons such as the applicants in the main proceedings in a centre located in its territory but not at the border.

The Court holds that EU law applicable to asylum applications processed in accordance with the border procedure does not prohibit Member States from detaining the applicants in places that are not geographically located at the border.

The Member States may also keep applicants for international protection in detention in the same places after the expiry of the time limit applicable to border procedures, provided that the grounds and conditions for that continued detention and the guarantees laid down by EU law to protect the rights of those applicants are complied with, in particular by informing those applicants of the change in their legal situation.

Furthermore, the Court holds that the investigative steps taken during the border procedure retain their validity in subsequent procedures, without prejudice to the possibility for the applicants to make further representations, in particular where there are elements which it was impossible to submit to the competent authority in the course of the border procedure.

The Court points out that the detention or continued detention of asylum applicants may be practised only where it is necessary, proportionate and limited to the period necessary, which the competent authority must ascertain in each case. Therefore, it cannot be automatic and systematic."