It's not just Republican senators who oppose an amendment allowing defense contractor employees to sue over rape in US courts.

It's also the Pentagon itself.

An amendment put forth by Sen. Al Franken (D-MN) sought to allow victims of rape to sue over their treatment in the US court system, after revelations that a KBR employee could only seek redress through arbitration, as outlined in her employment contract.

Thirty Republicans voted against the amendment, which passed the Senate 68-30.

The provision was sparked by the gang-rape of a 19-year-old KBR employee by her coworkers in Iraq. After returning to the United States, Jamie Leigh Jones found she couldn't sue the company because of a clause in her employment contract.

A message sent to senators Oct. 6, discovered by reporter Ryan Grimm, shows that Obama's Pentagon opposed the measure.

"The DoD opposes the proposed amendment," a message from the administration said.

A White House spokesman told Grimm they supported the amendment's "intent."

"We support the intent of the amendment, and we're working with the conferees to make sure that it is enforceable," spokesman Tommy Vietor said.

"The Department of Defense, the prime contractor, and higher tier subcontractors may not be in a position to know about such things. Enforcement would be problematic, especially in cases where privity of contract does not exist between parties within the supply chain that supports a contract," the Pentagon's remarks added. "It may be more effective to seek a statutory prohibition of all such arrangements in any business transaction entered into within the jurisdiction of the United States, if these arrangements are deemed to pose an unacceptable method of recourse."

Speaking in opposition to the amendment, Republican Sen. Jeff Sessions (R-AL) said, "Congress should not be involved in writing or rewriting private contracts," saying the measure was a "political amendment at bottom, representing a political attack on Halliburton."

In a statement Monday, Sen. Bob Corker (R-TN) said descriptions of the amendment as purely "anti-rape" were overstated.

"This vote has been grossly misunderstood, oversimplified, and misreported," Corker spokeswoman Laura Lefler Herzog said in a statement. "Senator Corker, the father of two daughters, believes what happened to Jamie Leigh Jones is abhorrent and that the culprits should be prosecuted to the fullest extent of the law; further, he agrees that rape, battery, and intentional infliction of emotional distress should not be arbitrated, but the Franken amendment went far beyond the ill it was trying to remedy to encompass most possible employment claims."

Republicans argue that the amendment abrogates the ability of companies to draft private contracts.