WASHINGTON - Silicon Valley is escalating pressure on President Obama to curb the U.S. government surveillance programs that vacuum personal information off the Internet and threaten the technology industry's financial livelihood.

A coalition that includes Google, Apple, Yahoo, Facebook, and Microsoft lashed out in an open letter printed Monday in major newspapers and a new website, http://reformgovernmentsurveillance.com.

The crusade united eight companies that often compete fiercely against each other, but now find themselves banding together to limit the potential damage from revelations about the National Security Agency's snooping on Web surfers.

Twitter Inc., LinkedIn Corp. and AOL Inc. joined Google Inc., Apple Inc., Yahoo Inc., Facebook Inc., and Microsoft Corp. in the push for tighter controls over electronic espionage. The group is immersed in the lives of just about everyone who uses the Internet or a computing device.

As the companies' services and products have become more deeply ingrained in society, they have become integral cogs in the economy.

Their prosperity also provides them with the cash to pay for lobbyists and fund campaign contributions that sway public policy.

Monday's public relations offensive is a byproduct of documents leaked over the last six months by former NSA contractor Edward Snowden.

The records reveal that the NSA has been obtaining e-mails and other personal data from major tech companies under secret court orders for the last five years and scooping up other data through unauthorized hacking into data centers.

Monday's letter and the new anti-snooping website represent the technology industry's latest salvo in an attempt to counter any perception that they voluntarily give the government access to users' e-mail and other sensitive information.

Although the campaign is ostensibly directed at governments around the world, the United States is clearly the main target.