President Barack Obama's plan to address border security and humanitarian concerns along the U.S.-Mexico border is coming under scrutiny on Capitol Hill.

The president says $3.7 billion in emergency funds are part of "an aggressive, unified, and coordinated Federal response" to an "urgent humanitarian situation" on the southwest border.

At a Senate Appropriations Committee hearing Thursday, Sec. of Homeland Security Jeh Johnson said without immediate action key border security and enforcement funding could run out by the end of the summer.

"Doing nothing is not an option," Johnson said. "At our current burn rate within the Department of Homeland Security, [Immigration and Customs Enforcement] will run out of money in mid-August. Given the added transportation costs, given the added enforcement costs, customs and border patrol will run out of money by mid-September."

The proposal makes around $1.1 billion available to ICE to help cover the costs of detention, prosecution and removal for the surge undocumented immigrants. It also includes $1.8 billion in funding to help the Department of Health and Human Services care for the estimated 52,000 unaccompanied minors who have crossed the border since October.

"To address the associated challenges, HHS has put together a two prong strategy for our part," HHS Secretary Sylvia Mathews Burwell told lawmakers Thursday. "One is first to drive down the length of time that children remain in shelters, the other is to expand our shelter capacity."

Despite Thursday's testimony, Republicans and Democrats still disagree that a new influx of cash is the best solution.

"What exactly is the $3.7 billion going to address? Will this request be the end, or will it be the beginning of many new requests for emergency funding?" Sen. Richard Shelby, R-Ala., said. "I personally have no confidence that pouring billions of dollars into our existing immigration system will solve the crisis."

"I believe that this is an emergency designation," said Sen. Barbara Mikulski, D-Md. "Our appropriations job now is to make sure that the resources to deal with this are met."

Speaker of the House John Boehner said Thursday Congress would not give the president a "blank check" to address the border crisis, suggesting for the second time that the president deploy the National Guard to aid the situation.