Immigration advocates on Thursday criticized the Trump administration's plan to conduct genetic testing on migrant children and parents separated as a result of its "zero tolerance" policy, saying the move is invasive and raises concerns over what the government might do with the biological data.

The federal government will be conducting the DNA tests — via a cheek swab — for every detained migrant child and then seeing if the DNA matches that of their purported parents, Cmdr. Jonathan White, assistant secretary for preparedness and response at the Department of Health and Human Services (HHS), said Thursday morning.

The move to collect DNA also raises serious concerns about consent for the children involved, said Jennifer Falcon, communications director for the immigrants rights group RAICES.

"They’re essentially solving one civil rights issue with another — it’s a gross violation of human rights," she said. "These are minors with no legal guardian to be able to advice on their legal right, not to mention they’re so young how can they consent to their personal information being used in this way?"

She added that the administration's fluctuating numbers on the number of separated children and the DNA testing showed "they did not do intake correctly and did not keep track of who they were separating."

She criticized the administration's reasoning that DNA tests were needed to quickly facilitate reunifications.

"They themselves have said they know where all the parents and children are so I think that’s bogus," she said. "When people are detained they are fingerprinted already so why do they need DNA swabs if these people wen through the proper intake process when they were detained?"

While DNA tests have sometimes been used in the past to help determine biological relationships when identifying documents are not available, applying them to such a large number of families is new, noted César Cuauhtémoc García Hernández, an associate professor at the University of Denver's Sturm College of Law who writes about criminal and immigration law.

Migrant children walk off a bus at the Catholic Charities' Msgr. Bryan Walsh Children's Village in Cutler Bay, Florida on June 21. Brynn Anderson / AP

"To apply it categorically to an entire population of people who have been separated by the government — that is a new addition to what the Trump administration is doing to immigration law enforcement," he said.

The government is reviewing cases of the under 3,000 children in its care who were separated from their parents, Health and Human Services Secretary Alex Azar said during a news teleconference.

García Hernández said that instead of the mass DNA testing, administration officials should add more human resources to facilitate determining parental relations.

"They need to put in as many resources to fix the problem as they did creating it," he said.

Lee Gelernt, deputy director of the American Civil Liberties Union’s Immigrants’ Rights Project, said in a statement to NBC News that the government should limit its use of such DNA tests and that the tactic raises issues of consent and privacy.

"We do not believe the government should be giving mandatory DNA tests in all reunification cases [but] should instead limit DNA tests to those cases where there is a genuine reason to doubt parentage, parentage cannot be established by any other means, and the parent agrees to the test," said Gelernt.

And, he added, "where DNA tests are appropriately used, the results should be expunged from government records once reunification is accomplished, and not be used for any other purpose than reunification."

Under the Obama administration, HHS officials warned that even requiring fingerprinting for sponsors could scare parents or other relatives who are in the country illegally away from claiming their children.

The HHS' White said Thursday that because the administration was restricted by the reunification time frame ordered by a judge last week, the typical verification process of using identifying documents and working with consulates in a migrant's home country would not be feasible.

Children under 5 must be reunited with their parents within 14 days after the judge's order and children older than that within 30 days. That means the first deadline is Tuesday, July 10 — and the government said Thursday it has about 100 such young children in its facilities.

"Because of the compressed time frame, the typical process of using documentations is not going to be completed within the time frame allowed in this case by the court decision for the great majority of these children," White said. "And for this reason the decision has been made to use the faster process of DNA verification to confirm that biological relationship."

The administration has also said the DNA tests will help protect children from potential traffickers.

White said "the DNA results are being used solely for that purpose and no other," but García Hernández said it remained unclear how long HHS would keep the DNA information and whether they would share it with other agencies — creating potential privacy concerns.

"There’s just no reason why anyone would assume they will not share it with" agencies such as the Department of Homeland Security, the FBI or others, he said.

García Hernández added it was also unclear if other family members, such an aunts, uncles or cousins, who crossed the border illegally with children would be counted in the biological matches.

Because of the violence plaguing Central America, it is possible that some children were adopted and/or came with caretakers who were not their parents or even their biological relatives, he noted.

"There’s a lot of reasons why kids would have parents who would not have a biological relationship, especially in places that have been experiencing high degrees of violence for many, many years like Central America where families shave been scattered by the gang violence that many individuals are now fleeing," he said.

"So it would not at all be an unusual here for children being raised by people who are not biologically their parents or who may not be biologically related to them whether it was a formal adoption or not."