This post has been updated to reflect the status of the equivalent funding bill in the Senate

A little-noticed provision of a bill that has to pass in order to keep the federal government’s lights on could kill one of the few tools designed to stop the torrent of American guns flowing across the border with Mexico.

As Congress reconvenes for its summer sprint, legislators could vote as soon as this week on an omnibus budget package to fund the federal government in 2018. One part of that package is the Commerce, Justice, Science Appropriations Bill, approved by the full Appropriations Committee on July 13. And attached to that bill is a rider which would prohibit the Bureau of Alcohol, Tobacco, Firearms and Explosives from using any funds to enforce a rule requiring gun dealers in Southwestern border states to report bulk sales of rifles and shotguns.

The language in question appears in Section 537 of the bill, and reads:

None of the funds made available by this Act may be used to require a person [licensed by the ATF to sell firearms] …to report information to the Department of Justice regarding the sale of multiple rifles or shotguns to the same person.

Commerce, Justice, Science Appropriations Bill

Bulk purchases are considered red flags for possible trafficking activity. Alerted to buyers of multiple long guns, ATF agents investigate further and look for other signs of gun running like straw purchasing, or repeated purchases made by members of one family.

In the eight months after the reporting rule went into effect in 2011, the ATF initiated more than 120 investigations and recommended charges against more than 100 defendants in 25 cases, according to a 2013 report by the Center for Public Integrity. Peter Forcelli, an ATF agent who worked on international trafficking enforcement at the time, told the Center for Public Integrity that the rifle-sale reporting requirement “gives us a head start to investigate potentially unlawful sales.” (Reached by The Trace on July 24, the ATF said it was unable to immediately provide updated figures.)

The Obama administration imposed the mandate rule in response to skyrocketing violent crime in Mexico and Central America, unleashed by drug cartels with a fondness for the semiautomatic rifles so popular in the United States. American guns are easily smuggled in cars or shipping containers as they head south, free from the same level of scrutiny applied to vehicles and shipments traveling from Mexico into the United States.

Of the 102,339 crime guns seized by Mexican authorities between 2010 and 2015 and submitted to the ATF for tracing, approximately 70 percent originated in the United States. American guns also account for more than 48 percent of weapons seized in El Salvador, which along with Guatemala and Honduras comprise the volatile Northern Triangle countries of Central America.

Policymakers, law enforcement, and diplomats in Latin America have pleaded for years for the United States to tamp down the flow of weapons, which contributes to violence so severe that every year, hundreds of thousands of citizens from the region flee to the United States as refugees. The multiple-rifle reporting rule is the only regulatory tool specifically designed to address the epidemic of gun-running over the Southwestern border.

The National Rifle Association has had the rule in its crosshairs for years. The gun group went to court to try unsuccessfully to have it overturned, and its Republican allies in the House have attached riders identical to this year’s version to annual appropriations bills in every budget cycle since 2012. Past Senate budget bills have not included the rider gutting the multiple-rifle reporting rule, even after Republicans retook the upper chamber in the 2014 midterm elections.

What may be different in 2017 is that this is the first year during which the president on the other end of the budget process is Donald Trump, a staunch ally of the NRA who vowed at the group’s annual meeting this April, “I will never, ever let you down.”

The Senate counterpart to the Commerce, Justice, Science Appropriations bill approved by a full committee markup Thursday afternoon does not contain an equivalent provision. However, one could be added as an amendment once the bill reaches the Senate floor, or during the conference between the two chambers.

The election that brought Trump to the White House also expanded the GOP’s control of both houses of Congress. The NRA spent more than $50 million on federal races in the 2016 election, and has vocally claimed credit for Republican victories at the ballot box. Despite those electoral successes, the NRA’s political allies have not yet delivered on some of the group’s top policy requests, like a bill to enshrine a national right to carry a concealed weapon.

Gutting the border-state rifle-reporting rule could be an easy way for elected Republicans to show an important conservative constituency that it hasn’t been taken for granted. If GOP lawmakers can’t do that through the budget process, they have another route they can pursue.

Representative Evan Jenkins of West Virginia and Senator Luther Strange of Alabama both introduced bills earlier this year to erase the reporting of border-state rifle sales by statute. Strange’s bill is cosponsored by Texans John Cornyn and Ted Cruz — powerful senators who gave the effort to kill the reporting rule added clout when they leant their name to the legislation.