LONDON — Major technology companies, stung by revelations that the U.S. government collects people’s personal data on their networks, on Monday issued an open letter to President Barack Obama asking for tighter controls on surveillance.

As part of a global campaign to reform data collection, Google, Facebook, Apple and others said concerns over national security should be weighed against individual rights.

“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,” the letter said. “This undermines the freedoms we all cherish. It’s time for a change.”

The letter follows this summer’s disclosures by former National Security Agency contractor Edward Snowden, who leaked details of the secret programs that critics argue violate privacy rights. Intelligence officials say the NSA’s tactics have helped disrupt terror attacks. Officials also insist that the agency takes care not to look at the content of conversations or messages by U.S. citizens.

The letter is the latest salvo from the Big Tech companies in a campaign to counter any perception that they voluntarily give the government access to users’ email and other sensitive information. The stakes are high: The companies depend on the trust of legions of online users who attract digital advertising — the online industry’s lifeblood.

A similar group of companies signed an Oct. 31 letter to senior lawmakers supporting proposals in Congress that would provide more transparency about the national security orders under which online companies must provide data to the government. By addressing Obama directly this time, the companies may be able to draw greater public notice.

It was a shrewd move for the companies to disseminate the open letter through newspaper ads, said Daniel Castro, a senior analyst for the Information Technology and Innovation Foundation, a Washington, D.C. think tank.

By virtue of connecting directly with a massive proportion of the U.S. population, the companies “have a huge reach,” Castro said. “They want people to be supporting and rallying around this effort.”

The Silicon Valley companies also are waging an attack in the Foreign Intelligence Surveillance Court, where they are fighting to be allowed to reveal more details about how frequently the NSA has been seeking user data. U.S. law currently prevents the recipients of national security orders from breaking down the number of demands they get under the Patriot Act. The companies contend that restriction fuels the erroneous perception that the government has a direct pipeline to their users’ data.

The technology companies argue that officials should codify “sensible limitations on their ability to compel service providers to disclose user data” and to ensure that law enforcement and intelligence efforts should be transparent and accountable. It makes an appeal for respecting the free flow of information across borders, describing it as “essential to a robust 21st century global economy.”

Though the campaign is directed internationally, a letter on its website and published in U.S. newspapers struck at the United States government, whose surveillance methods have attracted particular scrutiny. CEOs and senior leaders of the companies weighed in, making it clear they were personally behind reform.

“Reports about government surveillance have shown there is a real need for greater disclosure and new limits on how governments collect information,” said Mark Zuckerberg, the CEO of Facebook. “The U.S. government should take this opportunity to lead this reform effort and make things right.”

Marissa Meyer, the chief executive at Yahoo, said the disclosures had “shaken the trust of our users.”

The letter was signed by AOL Inc., Apple Inc., Facebook Inc., Google Inc., LinkedIn Corp., Microsoft Corp., Twitter Inc. and Yahoo! Inc.

Obama has asked a panel of hand-picked advisers to report on the issue this month and recently said he’ll propose the NSA use “some self-restraint” in handling data. He maintains, however, that the NSA isn’t interested in reading people’s emails and text messages.

The technology companies have good reason to band together. The free flow of information is fundamental to their business models. Information on consumers is critical to advertisers. But consumers need to trust that their privacy concerns are safeguarded, said Joss Wright, a research fellow of the Oxford Internet Institute.

Technology companies are also concerned that governments outside the U.S., such as the European Union, might set tougher rules for businesses to protect the privacy of their citizens, Wright says.

“It’s potentially huge,” Wright said. “Other countries around the world could make it harder for (the companies) to carry on with unrestricted data gluttony.”

That data is not just from browsing the web or cellphones. The latest reports showed U.S. and British intelligence officers have even been spying on gamers by trawling data from popular online games such as World of Warcraft.

Privacy International, a U.K.-based charity, praised the industry effort and described it as a reminder that there are gross violations of the right to privacy as governments access and share bulk metadata records.

“It is time for drastic changes to how intelligence is regulated, conducted and overseen, and we welcome these companies’ contribution to this debate,” Privacy International said in a statement.

Others, however, noted Silicon Valley’s stance probably had more to do with profit than principle.

“It sure would have been nice if the tech companies had been loudly supporting intelligence reform before Snowden’s disclosures,” said Chris Soghoian, a senior analyst with the American Civil Liberties Union.