The European Union is demanding assurances that Europeans are not having their rights infringed by a massive US surveillance programme.
Justice Commissioner Viviane Reding plans to raise the concerns with US Attorney General Eric Holder on Friday.
Last week a series of leaks by a former CIA worker led to claims the US had a vast surveillance network with much less oversight than previously thought.
The US insists its snooping is legal under domestic law.
The Obama administration is investigating whether the disclosures by former CIA worker Edward Snowden were a criminal offence.
Edward Snowden’s employer, defense contractor Booz Allen Hamilton, said on Tuesday it had fired the 29-year-old infrastructure analyst for violating its ethics code.
US officials say the snooping programme known as PRISM, revealed in last week’s leaks, is authorized under the Foreign Intelligence Surveillance Act (FISA).
It gives the US National Security Agency (NSA) the power to obtain emails and phone records relating to non-US nationals.
But details about the individuals targeted under the act remain secret, and there are concerns the NSA is overstepping its powers.
Documents leaked to the Guardian and Washington Post newspapers claimed the US authorities had direct access to the servers of nine major US technology firms, including Apple, Facebook and Google.
Edward Snowden told the Guardian that individual operatives had the power to tap into anyone’s emails at any time.
Although the firms have denied granting such access, saying they agreed only to legal requests, US officials have admitted PRISM exists.
One of the Guardian journalists who wrote the PRISM stories, Glenn Greenwald, has promised “more significant revelations” to come.
In the US, the controversy has focused on the possibility that conversations of US citizens may inadvertently be captured.
But overseas, governments and activists point out that US law provides foreigners with no protection.
Justice Commissioner Reding tweeted: “This case shows why a clear legal framework for the protection of personal data is not a luxury but a necessity.”
Edward Snowden is believed to be in hiding a day after he reportedly checked out of a Hong Kong hotel.
In the US, Senator Dianne Feinstein, the chairwoman of the Senate intelligence committee, said the American authorities were “aggressively” pursuing him.
The California Democrat also accused Edward Snowden of “an act of treason”.
The top Republican in the US House of Representatives, Speaker John Boehner, labeled Edward Snowden a “traitor”.
“The disclosure of this information puts Americans at risk,” he told ABC News on Tuesday morning.
“And it’s a giant violation of the law.”
The government began wireless wiretapping after the 9/11 attacks, but the surveillance policy expanded under President Barack Obama.