Hundreds of thousands of people could become eligible for deportation from the U.S. over the next two years if President Trump phases out an Obama-era program for certain undocumented immigrants, a move that reportedly may soon be announced. But the Trump administration may have already had an effect on who participates in the Deferred Action for Childhood Arrivals program, commonly known as DACA.

For months, some pro-immigrant groups have warned against sending in new applications for the program, saying that the detailed information given to confirm eligibility could be used to deport enrollees or family members in the future. And a new poll shows that some of the people who are already enrolled may be afraid to renew their applications as a result of that possibility.

An online survey of DACA recipients found that about 20 percent of respondents who were eligible to renew their status had not yet done so. Roughly 1 in 4 of that group cited fears that the government would use the updated details to identify them for law-enforcement purposes, according to the soon-to-be published report from United We Dream and other groups that was provided to FiveThirtyEight.

Of those who are in the program but not yet eligible for renewal, 28 percent said they would be less likely to reapply when the time comes because of law-enforcement concerns. The estimates are rough, because of the challenges inherent in polling undocumented people, but they provide a glimpse of the concern from some so-called dreamers that their personal information could be used for deportation.

We’ll have to wait for a clearer sense of whether the concerns over personal data have, in fact, kept many people from reapplying to the program. The next quarterly report including the number of actual applications and approvals, the first one to reflect data under the Trump administration, is expected to be released next week, according to a public affairs officer at the Department of Homeland Security.

But there’s reason to think fears about how their data will be used is as widespread as the survey suggests. Since Trump took office, some of the largest organizations that work with people eligible for DACA have been encouraging them to think carefully before applying for the protected status. The Coalition for Humane Immigrant Rights, which helps immigrants apply for various kinds of legal status, including DACA, has warned that it’s risky for people not already in the program to apply. They also warned people who are renewing to consult with a lawyer.

And it’s not just activist groups that have told potential applicants to be cautious. After the election, the University of California system issued similar guidance to students, writing that “Applying for DACA provides your contact information, immigration history, and other important information to DHS, which can then use that information to go after you or your family members that reside at your address,” in an online FAQ.

Meanwhile, a key date looms for the administration to make a decision on the program. Officials in 10 states have said they’ll sue the administration if it doesn’t end the program by Tuesday.

There’s no way to know whether the online survey, which was conducted by Tom K. Wong, a professor at University of California, San Diego in connection with several immigrant activist groups, is representative of DACA recipients at large because it’s impossible to randomly sample the group.

“There’s no directory to randomly select participants from,” said Wong. For that reason, researchers often partner with networks that support DACA recipients in order to conduct research on the group. Dreamers who respond to surveys are generally believed to be more educated than the group at large.

The Deferred Action for Childhood Arrivals program was enacted in 2012 by then-President Barack Obama through an executive action. Only a small share of the approximately 11 million undocumented people in the country qualify for the program. Among other things, they must have arrived in the U.S. before age 16, have continuously been in the country since 2007, have little to no criminal record, and be enrolled in the military or school or be a high school graduate. The Trump administration has continued to issue new and renewed work permits through the program, despite Trump’s campaign promises that he would end the practice.

But if even a small percentage of DACA enrolees opt not to renew their eligibility, it would mean thousands of people might lose their legal status. Nearly 800,000 people have been granted this status since the program began, the majority of the 1.3 million people currently eligible for the program, according to the Migration Policy Institute. Participants include medical students, lawyers, employees of large tech companies and college students.

But that status is only temporary, stretching for two or three years depending on when a person last enrolled. Some 110,000 people are up for renewal in 2017, according to an analysis by David Bier at the CATO Institute, a libertarian think tank, based on quarterly reports from the Department of Homeland Security. To apply for or renew DACA, applicants must send in what can be pounds of paperwork, often including information on where a person lives, names of family members, their school, travel and medical records. They then often go through biometric screening that involves providing fingerprints and photographs.

Because applications have been granted over a number of years, eligibility could phase out over time if the administration ended the program but allowed those with current permits to use them until they expire. Bier estimated some people would maintain their legal status through part of 2019, though for hundreds of thousands it could be as early as this year if DACA is ended.