Silicon Valley is escalating pressure on president Barack Obama to curb the US government surveillance programmes that sweep up personal information from the internet and threaten the technology industry's financial livelihood.
The crusade unites 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, LinkedIn and AOL joined 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.
The 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 information through unauthorised hacking into data centres.
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 government spies and other prying eyes.
The letter and the 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' email and other sensitive information.
Although the campaign is ostensibly directed at governments around the world, the US is clearly the main target.
"The balance in many countries has tipped too far in favour 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."
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.
By analysing search requests, web-surfing habits, social networking posts and even the content of emails, the companies are able to determine, for instance, the type of digital ads to show individual users. The NSA revelations have raised fears that people might shy away from some internet services or share less information about themselves. Such a shift would make it more difficult for companies to increase their ad revenue and, ultimately, boost their stock prices.
In a statement, Yahoo chief executive Marissa Mayer said the NSA disclosures had "shaken the trust of our users".
US intelligence officials have staunchly defended the electronic espionage, contending 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 US citizens.
Mr Obama has asked a panel of hand-picked advisers to report on the spying issue this month and recently said he will propose the NSA use "some self-restraint" in handling data.
White House spokeswoman Caitlin Hayden indicated the administration expects to address many of the concerns raised in the letter after Obama advisers complete their review. "As we have said repeatedly, we are committed to conducting intelligence activities with appropriate constraints, oversight, transparency and accountability," she said.