Thousands of people are expected to march on the National Mall in Washington, D.C. today to protest against the U.S. National Security Agency's surveillance program.

Organizers of the rally, the Stop Watching Us Coalition, want to end government spying on American citizens.

Their campaign comes amid increasing scrutiny of the NSA, with revelations this week that is has been spying on allies that include France and Germany.

The rally also coincides with the 12th anniversary of the U.S. Patriot Act. That law, pushed through Congress by the Bush administration after the Sept. 11, 2001, attacks, allows the FBI to issue national security letters without a judge's approval in terrorism and espionage cases.

The letters require telephone companies, internet service providers, banks, credit bureaus and other businesses to produce highly personal records about their customers or subscribers.

Former NSA contractor Edward Snowden's leaks about the agency's surveillance programs have raised new awareness of phone and internet interceptions carried out by the NSA, which has been in existence since the 1950s.

The NSA can find out what phone numbers Americans call, how long they talk, and listen to the content of some of those calls. The agency also has access to the computer servers of major U.S. internet providers and can look at things like emails, instant messages, Facebook posts, pictures and contact lists.

Rally organizers plan to present Congress with an anti-NSA a petition that has more than 570,000 signatures.

The group said the agency is operating "without any meaningful oversight" as it spies on personal communications.