
The European Court Of Justice's Advocate General, Henrik Saugmandsgaard, has said that bulk retention of data is only justified in cases of "serious crime".
However, commenting on a case taken against the UK, he said that such data retention can be in accordance with EUMember States' national laws.
In an opinion delivered ahead of a formal Court ruling on a case challenging Britain's right to retain data, Mr Saugmandsgaard said that a "general obligation to retain data may be compatible with EU law" but this is "subject to satisfying strict requirements".
In practice, the European Court Of Justice usually follows the view of the Advocate General.
"The fight against serious crime is an objective in the general interest that is capable of justifying a general obligation to retain data," said Mr Saugmandsgaard. But this obligation must be "strictly necessary to the fight against serious crime," and "proportionate".
In deciding whether proportionate, he said, EU states must respect the "essence of the right to respect for private life and the right to the protection of personal data laid down by the Charter [the EU Charter of Fundamental Rights]".
The latest decision means telecoms operators may be required to retain customer communications data as long as it is strictly necessary to fight serious crime and does not unduly interfere with privacy, an adviser to the top EU court said on Tuesday.
The types of data that can be retained include the date, time and duration of calls, and the source and destination of calls. However, the content of calls can not be retained, the advocate general said.
Yesterday's opinion referred to two cases in which data retention laws in Sweden and Britain were challenged on the grounds that they were no longer valid after the ECJ struck down an EU-wide data retention law in 2014 because it violated people's privacy.
However, national governments may oblige telecoms operators to retain communications data as long as there are strict safeguards to protect privacy, the advocate general said. (Additional reporting Reuters)