Plans by European Union countries to issue certificates showing that citizens have been vaccinated against Covid-19 should have a legal basis to ensure that they are necessary and proportionate, Reuters quoted the bloc’s privacy watchdogs as saying on Tuesday.

The European Data Protection Board (EDPB) and the European Data Protection Supervisor (EDPS) also warned against using data in such travel documents to create a central EU database.

Tourism-reliant countries such as Greece, Spain and Portugal are hoping that vaccine certificates will revive international travel and save this summer’s holiday season. While some countries want an EU-wide approach to the issue, others are planning national schemes.

“Any measure adopted at national or EU level that involves processing of personal data must respect the general principles of effectiveness, necessity and proportionality,” EDPB head Andrea Jelinek said in a statement.