Senior US spy chiefs are appearing before the House intelligence committee to answer questions about the US eavesdropping on other governments.
Earlier the US Senate announced a major review of the country's surveillance operations, after outrage that German Chancellor Angela Merkel had been tapped.
The US has denied using intelligence for economic advantage, and insists it was for security purposes.
The US Senate has called for an end to eavesdropping on leaders of so-called "friendly nations"
Director of National Intelligence James Clapper has told the House Intelligence committee that surveillance is used to protect American citizens.
As Americans, we face an unending array of threats to our way of life – more than I've seen in my 50 years in intelligence," he said.
"We need to sustain our capability to detect these threats. We certainly welcome a balanced discussion about national security and civil liberties - it's not an either / or situation. We need to continue to protect both."