The European Union top court struck down a law that required telecom providers to collect subscriber's personal metadata and hold it for up to 2 years, saying it goes against citizens' right to privacy.

The decision, issued by the European Court of Justice (ECJ) on Tuesday, addresses the conflict between citizens' civil liberties and the law enforcement agencies' need to access information to investigate crimes. In the wake of the Edward Snowden revelations, countries all over the world are struggling to strike that balance.

The ECJ found that the 2006 European Data Retention Directive directive, issued after the terrorists attacks in Madrid and in London, leaned to far on the side of law enforcement.

"The fact that data are retained and subsequently used without the subscriber or registered user being informed is likely to generate in the persons concerned a feeling that their private lives are the subject of constant surveillance," the court said in a statement.

The directive was implemented to harmonize practices of data-retention across Europe, with the goal of giving European law enforcement better access to all kinds of telephone and Internet metadata. The ECJ argued that the directive's broad scope violated citizens' "fundamental rights to respect for private life and to the protection of personal data," and was thus "invalid."

In fact, the court ruled that the data collected, "taken as a whole, may provide very precise information on the private lives of the persons whose data are retained, such as the habits of everyday life, permanent or temporary places of residence, daily or other movements, activities carried out, social relationships and the social environments frequented."

The case reached the ECJ after activists at Digital Rights Ireland and the Austrian Working Group on Data Retention brought challenges against their respective countries.

Civil liberties advocates across Europe celebrated the ruling.

"It is not, and never was, proportionate to spy on the entire population of Europe," London-based Internet advocacy group Privacy International said in a press release. "It is right and overdue that this terrible directive was struck down."

The Open Rights Group, another European advocacy organization, hailed the decision as "a major victory for privacy rights."

The ECJ's decision, however, won't have an immediate effect since many EU countries have already adopted the directive with their own national laws. But the ruling opens the door for challenges in every country.

A spokesperson from the European Court of Justice tweeted that it's now up to each country to react to the ruling "as they see fit."

Open Rights Group, for example, said it will consider a legal challenge in the UK. The high courts in Germany, Romania and the Czech Republic had already struck down their respective data-retention laws in the past.

In the United States, there is no data-retention law that compels companies to keep data, although many telecom and Internet providers retain certain data for billing and other business-related purposes. That is how the NSA, for example, is able to collect virtually all Americans' phone records, by requesting access to that stored data.

Privacy International as well as other observers hope this ruling can push more countries in Europe, and even across the world, to stop blanket data-retention practices.

"This ruling not only demolishes communications data surveillance laws across Europe, but sets a precedent for the world," the group said. "The widespread and indiscriminate collection of information has been, and always will be bad law, inconsistent with human rights and democratic values."

"Considering this decision comes after the NSA revelations, I think it sends a message across the ocean as well: no limitations on citizens' fundamental rights will be accepted, unless they are proportionate," Francesco Micozzi, an Italian lawyer who specializes in Internet law, told Mashable.

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