Sen. Bernie Sanders (I-Vt.) and Rep. Raúl Grijalva (D-Az.) have 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 Washington Post reports. The request to Homeland Security Secretary Jeh Johnson suggests that homeland security officials could face greater pressure to revisit their use of the for-profit facilities. It comes 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 U.S. are private, run either by Corrections Corporation of America or the GEO Group. Sanders and Grijalva say that 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 on detention. In 2014, it entered into pricey contracts to detain Central American women and children seeking asylum.