More than a quarter of the Senate’s members asked the top intelligence official on Friday to release more information on the government’s bulk collection of data on Americans’ communications.

Led by Senator Ron Wyden, an Oregon Democrat who has long hinted at the broad scope of the classified surveillance, the group of 21 Democrats, four Republicans and one independent sent a letter to James Clapper, the director of National Intelligence, requesting public answers to a series of questions about how the data is collected and used.

Former National Security Agency contractor Edward Snowden faces espionage charges in the United States for taking records about secret surveillance of Internet and phone traffic and releasing them to the Guardian and The Washington Post.

Snowden, who has requested political asylum in Ecuador, has not been seen since he arrived in Moscow on Sunday. Russian officials said he was in a transit area at Sheremetyevo airport.

The release of the material has prompted a firestorm of concerns about the extent of government data tracking as well as questions about lawmakers’ role in approving the legislation that allowed the data collection