A free health-care program in an impoverished part of the world sounds like a welcome development. But the “Physicals for All” project in China’s Xinjiang Uyghur Autonomous Region is not what it seems, according to a Human Rights Watch report published today.

Starting in 2016 and running annually from July through November, the project, though operated by health departments, is actually used by police to collect citizens’ DNA samples and blood types. This year, the program gathered such data on over 18 million residents in the region.

In recent years Chinese authorities have struggled to maintain control in the politically restive region, which is home to 10 million Uyghurs and other predominantly Muslim ethnic minorities. Other measures have included bans on veils, “abnormal” beards, and religious activities in schools, plus a requirement to provide a DNA sample to get a passport. In one part of the region, authorities required that all vehicles have a GPS system for government tracking—or be denied service at gas stations.

The Physicals for All program stands out for the way it’s been characterized as a free benefit for a poor region, and important to stable development (link in Chinese). ”What’s transmitted to the public via media and social media do not mention DNA collection in Physicals for All,” wrote HRW researcher Maya Wang in an email to Quartz.

HRW points to government guidelines (link in Chinese) on “population verification” that include instructions on offering medical checkups like Physicals for All. They state health workers should collect accurate data on anyone between the ages of 12 and 65. There is no age range, however, for individuals deemed dangerous by authorities, in which case any immediate family members should be also be given the physicals.

Although Physicals for All is touted as a voluntary program (link in Chinese), some residents told HRW that that wasn’t the case. One Uighur said his neighborhood committee demanded participation, warning that any absence would be considered “political disloyalty.” He added he had not received the results of his physical.

In recent years, China has been stepping up efforts nationwide to collect personal information—including intimate relationships, delivery records, and biometric data—from not only people it considers potential threats, but normal citizens as well. Government databases now include such data on tens of millions of citizens, among them Uyghurs, migrant workers, and college students.