Eight of the nation's largest technology companies have called on President Obama and Congress to impose new curbs on surveillance after a series of revelations detailing how the National Security Agency (NSA) accessed and collected user data from their customers.

The eight companies -- Microsoft, Google, Apple, Facebook, LinkedIn, Yahoo, AOL and Twitter -- called on the United States to lead a worldwide effort to restrict online spying and offered a plan of their own in an open letter published in several U.S. newspapers Monday. A website, Reform Government Surveillance, was also set up to present the group's talking points.

Among the restrictions the letter calls for is an end to bulk collection of user information, including e-mail, address books, and video chats; reviewing of surveillance requests by an independent court with an adversarial legal process; public disclosure of government demands for user information, as well as their frequency and nature; and an international framework to govern lawful data requests across national boundaries.

"We understand that governments have a duty to protect their citizens. But this summer’s revelations highlighted the urgent need to reform government surveillance practices worldwide," the letter says, in part. "The balance in many countries has tipped too far in favor of the state and away from the rights of the individual — rights that are enshrined in our Constitution. This undermines the freedoms we all cherish.

"For our part," the letter continued, "we are focused on keeping user’s data secure — deploying the latest encryption technology to prevent unauthorized surveillance on our networks and by pushing back on government requests to ensure that they are legal and reasonable in scope."

Beginning in June, a series of leaked NSA documents published by the Guardian in Britain and The Washington Post in the United States, showed that the agency had collected information from millions of customers without the companies' knowledge and in many cases with almost no judicial oversight.

The NSA has repeatedly defending its surveillance practices, arguing that its efforts were concentrated on gathering intelligence against legitimate foreign targets in the war on terror, and not, as it put it, "sweep up communications that are not of bona fide foreign intelligence interest to the U.S. government."