Sen. Bernie Sanders (I-Vt.) and Rep. Raúl M. Grijalva (D-Ariz.) on Monday asked the Department of Homeland Security to end its use of privately operated detention centers, a step they said would save the government money and open the door for “more humane” alternatives.

The request — coming in a letter to Homeland Security Secretary Jeh Johnson — is hardly the first time politicians have criticized the use of privatized immigration detention centers. But it indicates how homeland security officials could face greater pressure to revisit their use of the for-profit facilities, coming days after the Justice Department said it would wind down the use of private prisons.

U.S. immigration authorities maintain a sprawling network of detention centers for immigrants who have committed crimes, are pressing asylum claims, or are awaiting deportation.

Stepping away from privatization would require a massive and difficult transformation for the federal government, forcing it to build its own detention centers, place more detainees in state and local facilities, or slash the number of immigrants being held. Nine of the 10 largest immigration detention facilities in the United States are private, run either by Corrections Corporation of America or the GEO Group.

According to the letter written by Sanders and Grijalva, among the 400,000 people held annually by the U.S. Immigration and Customs Enforcement agency, 62 percent are at private facilities. The agency spends more than $2 billion a year detaining individuals, and in 2014, it entered into particularly pricey contracts to detain Central American women and children seeking asylum.

“Given the impact on detainees, the high cost to taxpayers and the Department of Justice’s recent decision, we believe the Department of Homeland Security can and should immediately begin phasing out for-profit, privately run immigration detention facilities,” the letter said. “As each contract comes to the end of its term, the department should either decline to renew the contract or substantially reduce its scope.”

The letter raised concerns about safety at immigration detention centers, saying that “adults and children detained in private detention facilities often go without due process protections and proper medical care.”

The Justice Department’s decision last week was spurred in part by a critical report from its inspector general’s office that concluded that privately run facilities lagged behind federal prisons in terms of safety and security. That report, though, did not apply to the immigration detention facilities and looked only at the 14 privately run federal prisons.

In a statement, CCA spokesman Jonathan Burns said the letter represented “stale arguments peddled by familiar critics” and noted that ICE planned to continue using “safe, humane, and appropriate solutions” like the company’s facilities. He added that the inspector general’s report had “significant flaws” and is at odds with other reviews.

ICE said in a statement that it “remains committed to providing a safe and humane environment for all those in its custody. For individuals in its custody, ICE seeks to reduce transfers, maximize access to counsel and visitation, promote recreation, improve conditions of confinement and ensure quality medical, mental health and dental care.”

GEO, in a statement Monday, did not directly address the letter but also criticized the inspector general’s report, saying that it was “severely flawed” and failed to “account for significant differences in inmate populations housed in privately operated facilities versus public facilities.”

“Additionally, despite claims to the contrary, the report in fact shows lower annual per capita costs for privately operated facilities,” GEO’s statement said.

For both GEO and CCA, immigration detention in recent years has emerged as a growing part of their business models. In 2015, CCA made 51 percent of its revenue from the federal government. Of that amount, nearly half came from immigration detention contracts.