Reuters reports that Patrick Meehan, chairman of the House Subcommittee on Counterterrorism and Intelligence, wrote to the DHS saying: “Although there are clear advantages to monitoring social media to identify possible threats to our security, there are also privacy and civil liberties concerns implicit in this activity.”

Meehan, along with Democrat congresswoman Jackie Speier, said that social media was a “crucial source” of intelligence from around the world, but urged the department to be mindful of the rights of citizens.

DHS spokesman Chris Orton defended the use of the programme over the weekend. In a statement he said: “The Department of Homeland Security’s National Operations Center employs social media monitoring for situational awareness purposes only, within the clearly defined parameters articulated in our Privacy Impact Assessment, to ensure that critical information reaches appropriate decision-makers.”

The DHS system, The Washington Post reports, is not just raising concerns among Congress members. The site reports that a privacy advocacy group has also recently filed a suit against the department seeking more information about the programme and how it monitors websites.