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, Twitter and Microsoft lashed out in an open letter printed Monday in major newspapers and a new website, http://reformgovernmentsurveillance.com. The companies are immersed in the lives of just about everyone who uses the Internet or a computing device.

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.

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 emails 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.

Monday’s letter represents the technology industry’s latest salvo in an attempt to counter any perception that they voluntarily give the government access to users’ information.

“The balance in many countries has tipped too far in favor of the state and away from the rights of the individual,” the letter said. “This undermines the freedoms we all cherish. It’s time for a change.”