Zack Whittaker/CNET

NEW YORK -- Despite sweltering heat and barely tolerable humidity, hundreds marched through New York City on Thursday to protest against mass spying by the U.S. National Security Agency.

About 500 people met in Union Square to listen to a number of privacy advocates and civil liberties groups discuss Fourth Amendment rights as they stand today, in light of recent revelations about the U.S. government's spying capability.

The government has been embroiled in an international diplomatic crisis over its intelligence agencies' spying on foreign nationals. Former NSA contractor Edward Snowden blew the whistle on a number of programs the U.S. employs to acquire masses of data on citizens around the world, including those in the European Union.

According to the organizers, Independence Day is a poignant day to protest in support of citizens' constitutional rights for protection against unreasonable searches and seizures, which they claim have been eroded under both the Bush and Obama administrations.

The U.K. government was also embroiled in the NSA spying saga after its Cheltenham-based listening station GCHQ was found to have tapped undersea fiber optic cables, in an operation code-named Tempora.

And the European Parliament on Thursday voted to give the European Commission authority, should it wish to use it, to suspend data-sharing agreements between Europe and the U.S., including SWIFT banking data and passenger name records (PNR) data. The U.S. government believes PNR data is vital for preventing terrorists from landing in the U.S. Should the agreement be put on ice, it could ground planes between the two continents.

People of all ages, from children to elderly folk, joined in the march, which snaked through the midtown area of Manhattan. The police presence was heavy -- more so to control the traffic than the crowds. Many marchers were chanting slogans, but the atmosphere was relaxed and friendly.

More than 100 protests are being held around the U.S. and Europe, as far as San Francisco; Chicago; Washington, D.C.; London; and Munich, according to the Restore the Fourth group.

The protesters are calling for an end to dragnet surveillance conducted by U.S. intelligence agencies, an investigation into domestic spying, and accountability on the part of public officials for what the protestors call this "unconstitutional surveillance."

Also, in a move reminiscent of the anti-SOPA actions of 2012, dozens of popular and high-profile Web sites, such as Mozilla, Reddit, WordPress, and Imgur, joined in publicly protesting the scope and reach of the Patriot Act and the Foreign Intelligence Surveillance Act (FISA), which paved the way for NSA programs like PRISM.