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 are more often fierce competitors, but they 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.

Monday's public relations offensive is a by-product of documents leaked over the past 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 past five years and scooping up other data through unauthorized hacking into data centers.

Silicon Valley has been fighting back in the courts and in Congress as they seek reforms that would allow them to disclose more information about secret court orders. Several of the companies are also introducing more encryption technology to shield their users' data from prying eyes.

Although the campaign is ostensibly directed at governments around the world, the U.S. is clearly the main target.

"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.

Civil liberties aren't the only thing at stake. One of the reasons the technology companies have become a rich vein for crime-fighting authorities is that they routinely store vast amounts of personal data as part of their efforts to tailor services and target advertising.