By Sonia Moghe, Nick Valencia and Holly Yan, CNN

(CNN) -- Whether this practice is beneficial or unethical depends on who you ask.

DNA tests are being performed on children and parents to try to reunite migrant families who were separated at the US border, a federal official with knowledge of the reunifications told CNN.

"The safety and security is paramount, and it is not uncommon for children to be trafficked or smuggled by those claiming to be parents," the official said.

"To our knowledge, this is a cheek swab and is being done to expedite parental verification and ensuring reunification with verified parents due to child welfare concerns."

The source could not discuss how long the practice has been taking place, if the testing requires consent or if the DNA is stored in a database.

Aid group worries about possible surveillance

RAICES, a nonprofit in Texas that offers free and low-cost legal services to immigrants and refugees, called the move deplorable because collecting such sensitive data would allow the government to conduct surveillance on the children "for the rest of their lives."

"This is a further demonstration of administration's incompetence and admission of guilt. This further drives home the point we've been saying: They never registered parents and children properly," RAICES communications director Jennifer K. Falcon said.

Falcon also said it's not possible the migrant children -- some as young as two months old -- are giving their consent to DNA testing.

The organization said they'd never heard of conducting DNA tests to reunite families before and they don't support the move.

Blood tests have been reported, attorney says

Attorneys representing migrant families said some of their clients have been approached by people who identified themselves as health officials or were wearing military-style clothing.

"I was told [by my clients] that 'men in blue military uniforms' were performing and ordering the blood and saliva tests," said Sophia Gregg, an immigration lawyer at Legal Aid Justice.

Gregg said she's learned that those people work with the Office of Refugee Resettlement.

Some are also conducting lengthy interviews with parents about their children, asking questions such as where their children were born and whether they have distinguishing marks, another attorney told CNN.

Deadlines loom for reuniting families

The Trump administration faces continued scrutiny over what will happen to the undocumented families separated as a result of the administration's "zero-tolerance" immigration policy.

The policy, which called for all migrants who cross the border illegally to face prosecution, meant more than 2,500 children were separated from their parents in two months. Many were scattered in facilities across the country by the Office of Refugee Resettlement.

After widespread criticism over family separations, the Trump administration laid out a plan to reunite the parents and children. But it's still not clear how many families have been reunited, since officials have refused to release new numbers for more than a week.

Now, the Trump administration must meet several deadlines, laid out by a federal judge, to reunite the families:

By Friday: Officials must make sure every separated parent has a way to contact his or her child.

By next Tuesday: Separated children under age 5 must be reunited with their parents.

By July 26: All children must be reunited with their parents.