An effort by President Obama to transfer America's lethal, highly classified drone program from the CIA to the Pentagon appears to have been thwarted by lawmakers wielding a secret weapon of their own.

The Washington Post reported Wednesday that members of Congress inserted a provision in a classified annex to the $1.1 trillion government spending bill introduced this week that would restrict funding or authorization to transfer from one to the other.

The move is an unusual one for Congress, and the debate over it will be closed to a small circle because of the classified nature of the addendum.

President Obama, under considerable pressure from the left over the program's civilian deaths and potential violations of international law, has for some time sought a way to distance himself from the controversial program that has come to be seen as his signature foreign policy and national security tool.

However, many members of Congress, even some in the president's own party, are not in agreement with the transfer of authority.

Sen. Dianne Feinstein (D-Calif.), chairman of the Senate Intelligence Committee and a member of the Appropriations Committee, declined to offer comment in the Post report, but said last year that she had seen the CIA “exercise patience and discretion specifically to prevent collateral damage” and that she “would really have to be convinced that the military would carry it out that well.”

In Beltway circles, experts say that while the U.S. drone program will have minor adjustments as needed, major debate over the direction of the program concluded years ago.

“Realistically, the policy window for reforming how the U.S. conducts lethal counterterrorism strikes is closed in Washington,” says Council on Foreign Relations fellow Micah Zenko.

However, during his nomination hearings last February, CIA Director John Brennan said that lethal operations are a “last resort” and could distract from the agency's core mission of intelligence gathering.

Over the course of the spring, following Brennan's hearings, President Obama began laying the groundwork for the shift.

In a May 2013 speech on counterterrorism at National Defense University, Obama opaquely signaled that he would minimize the number of lethal strikes and that he was transferring the program from the CIA to the Pentagon — a move that some observers understood as an attempt to make the program more transparent.

Just weeks before Obama's speech, when the Obama administration declined to send a representative to a Senate hearing on drone operations, Sen. Dick Durbin (D-Ill.) said “more transparency is needed to maintain the support of the American people and the international community.” He added that the White House should provide details on its claim to “its legal authority to engage in targeted killings and the internal checks and balances involved in U.S. drone strikes.”