A growing number of Democratic lawmakers are sounding the alarm about a program launched by the U.S. Department of Health and Human Services to track the spread of the coronavirus.

The public health effort, dubbed “HHS Protect Now,” hoovers up vast amounts of data, including coronavirus test results, from the Centers for Disease Control and Prevention, as well as state and local sources. It also relies on technology from secretive Silicon Valley firm Palantir, better known for working with the U.S. military, national security agencies and immigration offices.

In a letter shared with The Washington Post and sent Tuesday evening to HHS Secretary Alex Azar, a group of Democratic U.S. senators and members of Congress, including Sen. Elizabeth Warren (D-Mass.) and Richard Blumenthal (D-Conn.), called for more transparency around the initiative. The letter questioned whether any of the data gathered would be shared with U.S. Immigration and Customs Enforcement to round up undocumented immigrants.

“We are concerned that, without any safeguards, data in HHS Protect could be used by other federal agencies in unexpected, unregulated, and potentially harmful ways,” the lawmakers.

Last week, members of the Congressional Hispanic Caucus brought up similar concerns, pointing to Palantir’s track record in assisting ICE in the arrests of hundreds of undocumented workers and caregivers of unaccompanied migrant children.

“Naturally, we have valid concerns on whether the existing surveillance framework Palantir has created to track and arrest immigrants will be supplemented by the troves of potentially personal health information contained within the HHS Protect platform,” the lawmakers wrote in a letter.

Katherine McKeogh, a spokeswoman for HHS, said in a statement that the agency does not share HHS Protect data with ICE. “We ensure the privacy and security of all data in the system and HHS Protect does not contain any personally identifiable information,” the statement said. McKeogh did not say whether any data would be shared with ICE or other agencies in the future. As a software provider, Palantir provides supporting technical services to HHS. Lisa Gordon, a spokeswoman for Palantir, said in a statement that all data collected by HHS Protect would remain under the control of HHS. “Palantir does not collect, broker, or share HHS data with other Palantir customers (including ICE-HSI) for any purposes other than those directed by HHS for their public health response efforts,” she wrote.

The two letters highlight the growing tension around the use of technology to track the coronavirus and the privacy issues it brings up. Private companies including Google, Apple and PricewaterhouseCoopers have created software meant to help curb the spread of the disease, and lawmakers have introduced legislation aimed at protecting personal data from abuse during the pandemic. The lawmakers say that while they encourage the use of technology to help fight the spread of the virus, they are also concerned about the increasing willingness of HHS to share health information with other agencies for immigration enforcement.

While the Health Insurance Portability and Accountability Act, or HIPAA, offers strict protections for individual health information, there are public health provisions that allow information sharing about communicable diseases. Public health agencies do not generally share that information with law enforcement agencies because doing so might discourage people from getting tested for communicable diseases. But at the federal level, under the direction of the Trump administration, that philosophy has changed, lawmakers said.

Both letters point to a 2018 case in which HHS’s Office of Refugee Resettlement gave ICE access to its records. The data was used by ICE to arrest hundreds of people who sponsored unaccompanied minors crossing the border. The letter sent Tuesday alleges the arrests led to immigrant children being held for longer periods of time in custody, which had a chilling effect on prospective sponsors.

By using public health information for law enforcement purposes, HHS risks eroding public trust in public health officials, the lawmakers said. “HHS must do everything in its power to ensure that the public can trust that the federal government will not misuse COVID-19-related data,” lawmakers wrote in the Tuesday letter.

Tuesday’s letter urges HHS to limit the sharing of data within the federal government, except for public health agencies. It also calls on the agency to disclose, in detail, exactly what data it is collecting and for what purpose.

Lawmakers also asked for details of how Palantir was awarded the contract for HHS Protect, which they said is worth $25 million. Palantir was co-founded by Peter Thiel, a powerful Silicon Valley investor and ardent supporter of President Trump.