Whenever lawmakers negotiate a final Defense spending bill for the coming fiscal year, one of the primary bones of contention will be money enacted in prior fiscal years.

Senate appropriators, in their fiscal 2017 measure (S 3000), would cut more than $4 billion in what they deem as excess funds leftover from prior spending laws, roughly twice the amount found by their House counterparts in their measure (HR 5293). Some of the programs that stand to lose already appropriated money are major weapons initiatives for rockets, ships and warplanes. And the gap between the Senate and House approaches on some individual programs runs into the hundreds of millions of dollars.

Despite the considerable sums at issue, the cuts to previously enacted funds have gone virtually unremarked upon in the press. The proposals are buried in tables located in the committee reports and usually go unexplained even there.

This shadowy subset of the defense budget looms large every year when the spending legislation is drafted. This year, it could be an even more pivotal issue, despite its low profile.

“This will absolutely be part of the negotiations in conference committee because what we are talking about are changes in policy that would redirect how DoD spends money Congress previously appropriated,” said Todd Harrison, a defense budget expert with the Center for Strategic and International Studies.