Republican lawmakers are challenging the Obama administration over a newly announced plan to expand the use of U.S. military bases to house illegal immigrant children, warning that it will put a strain on troops and threaten military readiness.

The Pentagon confirmed this week that Defense Secretary Chuck Hagel has approved a request from the Department of Health and Human Services to house an additional 5,000 minors at DOD facilities.

The announcement has fueled concerns that what was initially described as a short-term measure is becoming an open-ended commitment.

“It’s very evident that this is not a short-term solution,” Donelle Harder, a spokeswoman for Sen. James Inhofe, R-Okla., told FoxNews.com.

About 2,500 young border crossers currently are being housed in facilities at Fort Sill in Oklahoma, Lackland Air Force Base in Texas, and Naval Base Ventura County in California. Initially cast as a four-month mission, the timeline now has been extended through at least Jan. 31, 2015.

It’s not clear where the additional 5,000 will stay, but the Pentagon is conducting assessments to figure this out. Among the possibilities apparently is Maxwell Air Force Base in Montgomery, Ala.

Alabama lawmakers on Thursday revealed the existence of “ongoing talks” between HHS and DOD over using the Maxwell base, though no decision has been made. Alabama GOP Reps. Martha Roby and Mike Rogers wrote a letter to the heads of both departments opposing such a plan and urging them not to go forward. Further, the lawmakers threatened to use the emergency legislation on the border crisis being considered in Congress to block illegal immigrants from being housed at military bases.

"The housing, feeding and caring of immigration detainees would severely compromise the critical mission at Maxwell-Gunter,” they wrote.

The lawmakers echoed their colleagues in arguing that the housing of illegal immigrant children is a strain on military resources.

“Throughout the year, Maxwell-Gunter hosts thousands of Air Force personnel conducting time-sensitive training essential for our national defense,” they wrote.

Members of the Oklahoma delegation earlier this week voiced similar concerns that the DOD decision to allow another 5,000 illegal immigrant minors on bases would turn Fort Sill into a long-term holding facility.

Rep. Jim Bridenstine, R-Okla., said the request poses a “very real threat to U.S. military readiness,” noting the base is the “primary artillery training center for troops before deployment.”

“Secretary Hagel should not extend or expand the use of Ft. Sill as a UAC camp," he said in a statement.

Military bases are just one piece of the puzzle as the U.S. government scrambles to address the influx of illegal immigrant minors who are making the dangerous trek from Central America, through Mexico and across the U.S. border. A number of facilities, many of them non-military, have been repurposed by HHS officials to handle hundreds of them at a time, while their cases are processed.

In Washington, the presidents of Guatemala, Honduras and El Salvador were meeting with President Obama on Friday to discuss the crisis and possible solutions. Obama is seeking additional funding from Congress to address the influx and considering additional policy changes.

But some Republicans say the solution is to swiftly deport those currently being housed at facilities across the country to send a message to Central America that they cannot stay, and to reverse a 2012 policy giving a reprieve to some illegal immigrants who came to the U.S. as children. Republicans argue that policy has acted as a magnet, even though it does not technically allow any of those who recently crossed to stay in the U.S.

House Republicans have discussed mandating changes to that policy as part of the emergency spending bill being considered on the Hill. Obama wants $3.7 billion to help with the crisis, but Republicans are proposing a much lower figure.

On the Senate side, Inhofe and Sen. Ted Cruz, R-Texas, have introduced legislation blocking the administration from using taxpayer funds to expand the 2012 policy.

Fox News’ Justin Fishel contributed to this report.