Three top defense lawmakers are threatening to scuttle a pending deal between Washington and Tokyo on how U.S. forces will position themselves in the Pacific.
The Pentagon plans to officially roll out a new basing strategy to move the Marines that are in Okinawa to new facilities in Guam. The island is already home to Andersen Air Force Base and a U.S. Naval base.
Pressure to ship the Marines off of Okinawa has been building in Japan since discussions to restructure the 2006 basing deal with the United States began.
However, Congress could block funding for the new Okinawa-to-Guam deal until DOD can explain how it fits into the White House's new national security strategy in the Pacific and defense spending plan in Washington.
"We are mindful of the turbulence that this issue has brought to U.S.-Japan relations ... [but] it is essential that we get these important decisions right, and that they be guided by sound strategic concepts and fiscally sustainable plans," Sens. Carl LevinCarl LevinFor the sake of American taxpayers, companies must pay their fair share What the Iran-Contra investigation can teach us about Russia probe Senate about to enter 'nuclear option' death spiral MORE (D-Mich.), John McCainJohn McCainGraham: North Korea shouldn't underestimate Trump Give Trump the silent treatment Five key moments from Trump's first 100 days MORE (R-Ariz.) and Jim Webb (D-Va.) said in a letter sent to the Pentagon on Tuesday.
"No new basing proposal can be considered final" until those key strategic and funding questions are answered by the Pentagon, according to the letter.
Both Senators claim the department has "been less than forthcoming" in tying the basing plan to the national security strategy unveiled by President Obama in February.
The plan lays the policy groundwork for DOD to pivot from Afghanistan and the Middle East to the Asia-Pacific region.
"Based on the information we have received about this emerging agreement, we have many questions that have not been fully addressed," according to the letter.
Aside from information on how the plan will affect the Pentagon's shift to the Pacific, both lawmakers want details on potential alternatives to Marine Corps basing in either Guam or Okinawa.
They also want specifics on "firm cost estimates ... an analysis of logistical requirements, and environmental studies" for the new Marine Corps facility in Guam, according to the letter.
The demands laid out by McCain and Webb match the ones lawmakers included in the fiscal 2012 defense spending bill that blocked initial funding for the new facility in Guam.
The legislation shut off any additional funds for the move until DOD issued a report detailing the same information requested in Tuesday's letter to DOD.
The report, which Congress requested to be complete by the end of March, has yet to be completed, McCain pointed out during a March 15 hearing of the Senate Armed Services Committee.
Navy Secretary Ray Mabus told the Senate Armed Services Committee in March that a private firm has been selected to conduct the assessment, but that company had not been put under official contract with DOD at the time.
However, Marine Corps Commandant Gen. James Amos told the committee the services and DOD are confident the assessment is on track.