Knowing about government surveillance prompts people to self-censor what they say online, and avoid expressing controversial opinions, a new study suggests. The research, designed to look at the relationship between free speech and government surveillance, uses the “spiral of silence” communication theory, which states that people continuously try to detect the opinions of the majority, and may keep quiet about their own views for fear of being excluded.

The study, published in Journalism & Mass Communication Quarterly (pdf), used an online survey to measure how a variety of factors,including the possibility of government surveillance and the perceived opinions of other people, influenced a person’s willingness to speak out online about a charged political issue.

The study measured willingness to speak out as how likely the person was to engage with a fictitious news article shared on Facebook (by commenting, liking, sharing, or posting a similar one) about US airstrikes against ISIL. More than 250 people completed all parts of the online survey, and about half of those people (121) saw a disclaimer about government surveillance three times in their questionnaire which read:

The next section of the survey asks for your honest opinions about some controversial political issues. While we make every attempt to ensure your opinions are kept confidential, it is important to keep in mind that the National Security Agency does monitor the online activities of individual citizens, and these actions are beyond the study’s control.

The study found that among a majority of the respondents who felt that government surveillance was justified—about two-thirds of the subjects—believing that the government might be monitoring your messages had a strong effect on whether or not the subjects chose to voice their opinions. Those who believed they held the majority opinion—that most people agreed with them—were more likely to speak up online. But those subjects who believed they held a minority, unpopular opinion were more likely to self-censor and keep their point of view to themselves.

In other words, the group of people who felt surveillance was “necessary for maintaining national security and they have nothing to hide” changed their behavior when they believed the government was monitoring them, by “expressing opinions when they are in the majority, and suppressing them when they’re not.” And although the sample size is quite small, Elizabeth Stoycheff, the study’s author and assistant professor at Wayne State University, told Quartz that she finds these initial findings troubling.

“A lot more work needs to be done before we can conclusively show the implications that surveillance has on free speech, but the initial results presented here do not paint an optimistic picture,” she told Quartz. “Free speech for only those who espouse popular, majority opinions isn’t free speech at all.”