Every time you email someone overseas, the NSA copies and searches your message. It makes no difference if you or the person you're communicating with has done anything wrong. If the NSA believes your message could contain information relating to the foreign affairs of the United States – because of whom you're talking to, or whom you're talking about – it may hold on to it for as long as three years and sometimes much longer.

A new ACLU lawsuit filed today challenges this dragnet spying, called "upstream" surveillance, on behalf of Wikimedia and a broad coalition of educational, human rights, legal, and media organizations whose work depends on the privacy of their communications. The plaintiffs include Amnesty International USA, the National Association of Criminal Defense Lawyers, and The Nation magazine, and many other organizations whose work is critical to the functioning of our democracy.

But the effect of the surveillance we're challenging goes far beyond these organizations. The surveillance affects virtually every American who uses the Internet to connect with people overseas – and many who do little more than email their friends or family or browse the web. And it should be disturbing to all of us, because free expression and intellectual inquiry will wither away if the NSA is looking over our shoulders while we're online.

The world first learned of the existence of upstream surveillance from whistleblower Edward Snowden's spying revelations in June 2013. Since then, official disclosures and media reports have shown that the NSA is routinely seizing and copying the communications of millions of ordinary Americans while they are traveling over the Internet. The NSA conducts this surveillance by tapping directly into the Internet backbone inside the United States – the network of high-capacity cables and switches that carry vast numbers of Americans' communications with each other and with the rest of the world. Once the NSA copies the communications, it searches the contents of almost all international text-based communications – and many domestic ones as well – for search terms relating to its "targets."

In short, the NSA has cast a massive dragnet over Americans' international communications.

Inside the United States, upstream surveillance is conducted under a controversial spying law called the FISA Amendments Act, which allows the NSA to target the communications of foreigners abroad and to intercept Americans' communications with those foreign targets. The main problem with the law is that it doesn't limit which foreigners can be targeted. The NSA's targets may include journalists, academics, government officials, tech workers, scientists, and other innocent people who are not connected even remotely with terrorism or suspected of any wrongdoing. The agency sweeps up Americans' communications with all of those targets.

And, as our lawsuit explains, the NSA is exceeding even the authority granted by the FISA Amendments Act. Rather than limit itself to monitoring Americans' communications with the foreign targets, the NSA is spying on everyone, trying to find out who might be talking or reading about those targets.

As a result, countless innocent people will be caught up in the NSA's massive net. For instance, a high school student in the U.S. working on a term paper might visit a foreign website to read a news story or download research materials. If those documents happen to contain an email address targeted by the NSA – like this news report does – chances are the communications will be intercepted and stored for further scrutiny. The same would be true if an overseas friend, colleague, or contact sent the student a copy of that news story in an email message.

As former NSA Director Michael Hayden recently put it , "[L]et me be really clear. NSA doesn't just listen to bad people. NSA listens to interesting people. People who are communicating information."

That doesn't sound like much of a limitation on the NSA's spying – and it's not. Like many Americans, the plaintiffs in our lawsuit communicate with scores of people overseas who the NSA likely finds "interesting." For instance, researchers at Human Rights Watch depend on foreign journalists, lawyers, political dissidents, and witnesses to human rights abuses for information crucial to their advocacy and reporting back home. Wikimedia communicates with millions of people abroad, many of whom read or contribute to Wikipedia, one of the largest repositories of human knowledge on earth. We know, thanks to Edward Snowden, that the NSA is interested in what some of those users are reading.

The fact that upstream surveillance is supposedly focused on international communications is hardly a saving grace. Americans spend more and more of their lives communicating over the Internet – and more and more of those communications are global in nature, whether we realize it or not. An email from a woman in Philadelphia to her mother in Phoenix might be routed through Canada without either one knowing it. Similarly, companies like Microsoft and Google often store backup copies of their U.S. customers' emails on servers overseas, again with hardly anyone the wiser. The NSA is peeking inside virtually all of these.

Our plaintiffs have had to go out of their way to take measures, sometimes at a high cost, to protect their communications from their own government. Despite these precautions, the chilling effect is palpable. NSA surveillance makes it harder for the plaintiffs to gather information from sources who believe that by sharing information over the Internet, they are also sharing it with the U.S. government and the intelligence agencies it partners with. The work of human rights and free-knowledge organizations is profoundly undermined by this unconstitutional surveillance, and we're all worse off.

Upstream surveillance flips the Constitution on its head. It allows the government to search everything first and ask questions later, making us all less free in the process. Our suit aims to stop this kind of surveillance. Please join our effort to reform the NSA .