The administration of United States President Donald Trump has purchased commercial databases and software that tracks millions of mobile phones and used the information to crack down on undocumented immigrants in the US, the Wall Street Journal (WSJ) reported on Friday.

Citing sources familiar with the matter and documents it has seen, the WSJ reported that the US Immigration and Customs Enforcement agency (ICE) has made arrests based on the data, which helped identify the movement and location of undocumented migrants.

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According to the report, the US Department of Homeland Security (DHS) began purchasing location data back in 2017 from Venntel, a Virginia-based company, which declined to comment. The data is gathered through smartphone applications after users grant access to their locations.

The DHS and its agencies acknowledged buying access to the data, but did not discuss details about how they are using it in law-enforcement operations. US Customs and Border Protection (CBP) has said it has privacy protections in place and limits on how it uses location data. The agency says that it accesses only a small amount of the information, which is anonymised to protect the privacy of Americans.

"While CBP is being provided access to location information, it is important to note that such information doesn't include cellular phone tower data, is not ingested in bulk and doesn't include the individual user's identity," a CBP spokesman told the WSJ.

Using mobile phone data purchased from a private company raises major concerns about privacy.

The use of data purchased from a commercial company allows the government to bypass a 2018 US Supreme Court decision, which ruled that phone location data was a protected class of information that requires law enforcement to obtain a warrant.

"The report that the federal government is buying private, sensitive data to track down immigrants and carry out deportations is deeply troubling," Saira Hussein, a staff lawyer at the Electronic Frontier Foundation, told Al Jazeera. "And it’s only possible because of our society’s failure to protect people from companies that harvest and monetise their personal information. This report precisely illustrates the need for strong consumer data privacy laws."

In a statement issued on Friday, the American Civil Liberties Union (ACLU) called the news "detestable".

"DHS should not be accessing our location information without a warrant, regardless whether they obtain it by paying or for free. The failure to get a warrant undermines Supreme Court precedent protecting our most sensitive information, especially our cell phone location history, from unfettered law enforcement access," read the ACLU statement.

"We will be demanding the government turn over all records concerning this disturbing practice, which is just the latest example of the extreme lengths the Trump administration will go to carry out its cruel and heartless immigration policies."

Trump has made cracking down on immigration a focus issue of his administration. He has falsely described asylum seekers and other border crossers as con artists who "scam" the system.