The Department of Homeland Security has asked DoD to have 2,000 beds for illegal immigrants ready within the next 45 days — and that is just the start of what the agency has asked the military to be ready for.

“The Department of Defense has received a request for assistance from the Department of Homeland Security to house and care for an alien family population of up to 12,000 people. DHS requests that DoD identify any available facilities that could be used for that purpose,” the Pentagon said in a statement late Tuesday.

The formal request was necessary to enable DoD to begin the process of deciding how it will fulfill the request — either by tasking members of the active duty or reserves, or contracting out the support and eventually pursue reimbursement from DHS for the support.

DHS has already visited multiple locations in Texas and Arizona. Earlier this week Secretary of Defense Jim Mattis said Goodfellow Air Force Base in San Angelo and Fort Bliss in El Paso would be used to house unaccompanied immigrant minors and families who crossed the border. Last week, Time magazine reported that Camp Pendleton in California and Marine Corps Air Station in Yuma were also under consideration.

DoD is preparing to receive up to 20,000 unaccompanied minors, and according to Tuesday’s memo, will now prepare for 12,000 family members.

If there are no current buildings available on the bases, “DoD has been asked to identify available DoD land and construct semi-separate, soft-sided camp facilities capable of sheltering up to 4,000 people, at three separate locations. DHS prefers the facilities to be built in Texas, Arizona, New Mexico, or California.”

Within the next 45 days, however, DHS has asked DoD to be ready for the first 2,000 illegal immigrants, with a note that “a timeline will be developed to add additional capacity.”

It’s not the first time the bases have been used in this capacity.

In 2014, Lackland Air Force Base was used to detain immigrant children, and at the time, HHS installed a fence to separate the children from the rest of the base, a defense official said.

In addition, a complex with an 1,800-bed capacity was used in 2016 at Fort Bliss to house unaccompanied minors who immigrated to the U.S. And about 700 immigrant children stayed at Holloman Air Force Base in New Mexico that same year. The minors spent about a month at the facilities.