(CN) - The European Union's highest court on Thursday ruled that people must be given a chance to know how their personal data was used by police authorities in investigations against them.

The European Court of Justice's decision came in a case involving a Belgian man whose past involvement with protests prevented him from getting a security clearance certificate he needed in 2016 to work in the assembly of an annual EU international forum in Brussels.

In denying him the certificate, Belgium's National Security Authority based its decision on his participation in 10 demonstrations between 2007 and 2016. The man was referred to only by the initials BA in court documents.

In February 2020, the Human Rights League, a Belgian advocacy group, took up BA's case and filed a request to obtain detailed information about how BA's clearance certificate application was handled.

The advocacy group argued that BA was entitled to the information under an EU law passed in 2016 that gives individuals more rights over how their personal data is processed by law enforcement agencies.

The complaint was filed with a Belgian police supervisory authority set up in 2018 to oversee how law enforcement agencies handle personal data.

But the supervisory panel refused to hand over the detailed information to BA, arguing that he only had an "indirect right of access" to the data, according to court filings.

However, the police oversight board said it would look into whether his data was processed lawfully and declared it had the power to erase or amend information about him stored in the national police data bank.

In June 2020, the board said it had verified how BA's data was used, but it declined to provide any further information.

The Human Rights League then sued the oversight board, an entity called the Supervisory Body for Police Information. The rights group said it was unlawful for there not to be a way to appeal the oversight board's decisions.

An appellate court in Brussels asked the European Court of Justice in Luxembourg to weigh in on whether decisions by the Supervisory Body for Police Information can be appealed.

On Thursday, the EU high court sided with the plaintiffs and said a system for appeals against decisions by a supervisory board must be allowed.

The court said EU judicial systems must ensure courts can examine "all the grounds and the related evidence" used by police in processing data and also be empowered to determine whether data was used properly.

A "data subject must have an effective judicial remedy against the decision of that authority to close the verification process," the court said in its ruling.

The Human Rights League said in an email that it was studying ruling, but it had no immediate comment.

Courthouse News reporter Cain Burdeau is based in the European Union.

Source: Courthouse News Service