A privacy advocacy group is suing the Commerce, Justice and Homeland Security departments for information about its research into technology that could scan peoples’ tattoos to reliably identify them or link them to gangs.

The Electronic Frontier Foundation filed a lawsuit this week against participants in the “Tattoo Recognition Technology Program,” which taps academia and the private sector for help in building out systems that can analyze tattoos in detail for information about the person they adorn, potentially supporting investigations more than “traditional soft biometrics such as age, gender and race,” according to Commerce’s National Institute for Standards and Technology.

The technology could be used to identify individuals with similar tattoos who are potentially associated with the same criminal organization or to link a person’s tattoos to other images like graffiti, according to NIST, which heads the FBI-sponsored program.

Last year, EFF filed Freedom of Information Act requests for details about the program, but the participating organizations withheld some records and heavily redacted some that they shared, according to EFF. This year, EFF aims to double down on its demands that the information be made public.

This kind of technology “raises serious constitutional concerns” because tattoos represent a form of self-expression, including “our innermost thoughts, closely held beliefs, and significant moments,” EFF Stanton Fellow Camille Fischer said in a statement.

Law enforcement efforts to gather those images in a database could curtail citizens’ First Amendment rights to freedom of expression and speech; it also could impinge on freedom of association “when people are matched with others for government surveillance and investigative purposes, sometimes incorrectly.”

EFF is especially concerned about tattoo surveillance, as compared to other biometric identifiers that the federal government regularly collects such as fingerprints because tattoos are elective, Fischer added. “Individuals choose to put tattoos on their bodies to express themselves, in both visible and non-visible locations.”

Tattoo recognition has already led to concrete law enforcement action, according to EFF, citing a case this year in which Homeland Security initiated deportation proceedings against a Deferred Action for Childhood Arrivals member because of a tattoo associated with a gang.

“These types of false associations have led an increasing number of people to remove their tattoos,” EFF’s complaint notes. “Because a tattoo may be currently associated with criminal activity does not mean that the owner intended such association,” and former members who no longer participate in such activity might still carry the tattoos.

EFF also argues that NIST and the FBI are testing the technology on data sets containing images of tattoos gathered from prisoners without their knowledge or consent, pointing to documents released in a previous FOIA request.