Visiting an art exhibit featuring works about the U.S. war on terror or going to a lecture about Islam wouldn’t be cause for worry—unless you found out that the government was monitoring and keeping track of attendees. At that point, some people would be spooked and stay away, sacrificing their interests and curiosity to protect their privacy, not look suspicious, or stay off a list some intelligence agency might be keeping.

Government surveillance has that chilling effect—on our activities, choices and communications—and carries serious consequences. We argue in our lawsuit First Unitarian Church of Los Angeles, et al v. NSA that the government’s collection of phone records violates the First Amendment rights of our clients—churches and civil and human rights organizations—by discouraging members and constituents from associating and communicating with them for fear of being spied on.

Now two new studies examining the use of Facebook and Wikipedia show that this chilling effect is real. Both studies demonstrate that government surveillance discourages speech and access to information and knowledge on the Internet. What happens is that people begin to self-police their communications: they are more likely to avoid associating with certain groups or individuals, or looking at websites or articles, when they think the government is watching them or the groups/people with whom they connect. This hurts our democracy and society as a whole.

The Facebook study, published in Journalism & Mass Communications Quarterly, showed that people censor themselves on the social network, refraining from posting comments voicing minority views when they’re aware that the National Security Agency (NSA) monitors online activities.

Participants in the study were told of NSA monitoring and shown a fictional Facebook posting about U.S. airstrikes against ISIS. They were asked about their willingness to comment, share, and like the post, or create a new post about the same topic. They were also asked whether they supported or opposed U.S. airstrikes, what they thought most other Americans believed about the airstrikes, and whether surveillance is necessary for national security.

The study showed that people who are aware of government surveillance and support it are significantly less likely to speak out when their views differ from what they perceive to be the majority opinion. As Dr. Elizabeth Stoycheff, Wayne State University assistant professor of journalism and new media and study author, writes:

This is the first study to provide empirical evidence that the government’s online surveillance programs may threaten the disclosure of minority views and contribute to the reinforcement of majority opinion… These individuals expressed that surveillance was necessary for maintaining national security and they have nothing to hide. However, when these individuals perceive they are being monitored, they readily conform their behavior—expressing opinions when they are in the majority, and suppressing them when they’re not.

The Wikipedia study, to be published in an upcoming issue of the Berkeley Technology Law Journal, found a dramatic fall in monthly traffic to Wikipedia articles about terror groups and their techniques after the June 2013 disclosures of the NSA PRISM surveillance program by whistleblower Edward Snowden. The study looked at 48 Wikipedia articles that contained terrorism-related keywords tracked by the Department of Homeland Security, such as “suicide attack” and “dirty bomb.”

Article views dropped 30 percent after June 2013, which supports “the existence of an immediate and substantial chilling effect,” wrote author Jonathon Penney. He also found that monthly views continued to fall, suggesting that the chilling effects of NSA surveillance are long term. The study, he says, has “implications for the health of democratic deliberation among citizens” and the broader health of society.

The government itself uncovered evidence in a recent survey that its surveillance causes Americans to limit their online activity. The Department of Commerce’s National Telecommunications and Information Administration (NTIA) found that in a survey of 41,000 U.S. households that use the Internet, one in five avoided online activity because of concerns about data collection by the government.

These studies provide evidence of what we have long argued—our freedom to read what we choose online and communicate and associate with others privately is profoundly affected by the prospect of the government looking over our shoulder. It’s changed our behavior, whether that means not commenting on a Facebook post about terrorism, avoiding a Wikipedia page, or steering clear of certain organizations.

The stakes are high for the 24 diverse political and activist groups that are our plaintiffs in First Unitarian. They connect people to advance political beliefs, and sometimes take dissenting positions on issues. Government surveillance of phone records to and from these groups, which work with whistleblowers, dissidents, Muslims, patients, gun owners, laborers, and others, have hurt their ability to carry out their missions. Their members and potential clients simply don’t want to call them, visit them on the web, or email them when they know the government is watching. The Council on American-Islamic Relations (CAIR)-Ohio, a community service and civil rights organization that assists Muslim facing racial profiling, harassment, and discrimination, has seen a decrease in communications from its constituency of Muslim Americans. Calguns, a group that assists California gun owners in exercising their rights, has also experienced fewer communications from members who want their communications with the group to be confidential. Human Rights Watch, another plaintiff, says fewer people are reporting human rights abuses—the organization can no longer guarantee security and confidentiality in their communications and those people contacting the group fear retaliation.

We’ve documented these and other affects of the government surveillance in our court filings. We argue that phone record collection violates our clients’ freedoms to associate with others to advance political beliefs. Their work is hampered by the fact that people are deterred from contacting them and they can’t guarantee confidentiality because of government surveillance.

Penney points out that courts, legal scholars, and researchers have been skeptical about the extent and even the existence of the chilling effects of government surveillance. We think these studies strongly support that phone record collection has discouraged Americans from communicating and speaking out, and should put that skepticism to rest.