WASHINGTON – Eight of America’s largest technology companies have called on President Barack Obama and Congress to impose strict new curbs on surveillance that, if enacted, would dramatically reshape intelligence operations that U.S. officials have portrayed as integral to the war on terrorism.

The uncommonly unified front — featuring companies that compete fiercely on business matters — underscored the deep alarm among technology leaders over revelations that the National Security Agency has collected user data far more extensively than the companies understood, in many cases with little or no court oversight.

In a letter to U.S. leaders published in several newspapers Monday, the coalition calls for an end to bulk collection of user information — such as email, address books and video chats — and for the enactment of significant new protections when courts consider specific surveillance requests.

“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. “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.”

The signers are Microsoft, Google, Apple, Facebook, LinkedIn, Yahoo, AOL and Twitter.

The proposals include a call for strong judicial oversight and an adversarial process for surveillance requests, including at the secretive Foreign Intelligence Surveillance Court.

The proposals bring the companies closer to the views espoused by privacy and human rights advocates, as well as to the USA Freedom Act, sponsored by Wisconsin Rep. James Sensenbrenner, a Republican, and Vermont Sen. Patrick Leahy, a Democrat. It is one of several bills drafted in response to the controversy over the revelations.

Reports in The Washington Post and in Britain’s Guardian newspaper, based on documents provided by former NSA contractor Edward Snowden, have shaken the tech industry since June and imperiled multibillion-dollar businesses that rely, at least in part, on user trust. Most troubling, industry officials say, was a Post report in October detailing how the NSA and its British counterpart were taking massive flows of information directly from the private communications links among data centers operated by Google and Yahoo.

Backlash has run particularly strong in Europe and Brazil, where government officials have reacted with fury to news that the NSA gained access to vast amounts of personal information about their citizens with little of the legal protection afforded to U.S. citizens.

“Recent revelations about government surveillance activities have shaken the trust of our users, and it is time for the United States government to act to restore the confidence of citizens around the world,” Yahoo’s chief executive, Marissa Mayer, said in a statement.

There has been a major push for new laws in several nations to limit international data flows in ways that industry officials say could hobble the functioning of the Internet. Consumer advocates have pointed out that government surveillance systems benefit from the voracious data collection done by private companies, which gather information to more precisely target the advertising that provides much of the industry’s profits.

U.S. intelligence officials have staunchly defended their surveillance practices. In a statement last month, the NSA said that efforts are focused on gathering intelligence against legitimate foreign targets, “not on collecting and exploiting a class of communications or services that would sweep up communications that are not of bona fide foreign intelligence interest to the U.S. government.”

Amid the revelations about NSA data collection, several major technology companies have embarked on initiatives to encrypt data in hopes of thwarting government spying. Companies also have pushed for greater transparency in surveillance requests so that they can offer more detailed accounts of the information they are compelled to turn over to government officials.

But Monday’s initiative goes further still by calling for substantive changes in the nation’s surveillance systems themselves and urging that other countries undertake similar reforms. The tech industry has emerged in recent years as one of the more influential in Washington, after years when companies often were content to stay on the legislative sidelines and avoid conflict.

“This united call for surveillance reform is a game changer,” said Leslie Harris, president of the Center for Democracy and Technology, a D.C.-based advocacy group that receives some industry support. “Bringing these powerful voices to this really important fight is going to rebalance the scales.”