With the the passage of a contentious $1.1 trillion federal spending package last night, the US House of Representatives may have effectively made Washington, DC the first unregulated zone for legal marijuana in the United States.

Earlier in the week, a deal struck between Senate Democrats and House Republicans effectively blocked a law legalizing marijuana in the District by attaching a rider to the 1,600-page federal spending bill. Congress controls DC's purse strings, and the rider effectively barred DC from using federal funds to implement the recently passed Initiative 71.

That measure, which 70 percent of DC voters voted in favor of last month, permits residents and visitors in the capital who are over 21 to possess up to 2 ounces of marijuana and grow up to three plants in their homes.

Since 1973, DC residents have had the power to elect their own mayor and city council, but Congress retains the power to override DC laws up to 60 days after they have been passed. Congressional overrides are exceedingly rare — but since Congress controls DC's budget, it can block laws from going into effect by quietly adding provisions to the federal budget, as it appears to have done this week.

"We have a battle on our hands whenever [Congress] thinks they can come in and influence us and how we govern ourselves," said DC Councilmember David Grosso, who sponsored a marijuana regulation bill that passed the DC council last year. "This is a blow to DC in general, a blow to home rule and our freedoms and democracy. Its frustrating."

All of that said, legalization is still very much a possibility in DC thanks to a potential loophole in the language of the measure attached to the spending bill.

The rider prevents the District from spending money to "enact any law, rule, or regulation to legalize or otherwise reduce penalties" related to marijuana. But as Eleanor Holmes Norton, DC's non-voting delegate to Congress, points out, that does not actually repeal legalization since — depending on legal interpretation — the law was already "enacted" when it was passed by DC voters.

"[Initiative 71] did not require enactment of any rules for its implementation," Holmes arguede before the House Rules Committee on Tuesday. "Therefore, it can be argued that the legalization of small amounts of marijuana can proceed."

Grosso, who is a longtime advocate for legalization in DC, agrees. "We've spoken to our attorneys here at the DC Council and… I'm confident that Initiative 71 can move forward in accordance with that [reading]," he told VICE News.

However, doing so would conflict with the position taken by the US Justice Department, which still classifies marijuana as a Schedule 1 illegal substance. In order to reconcile federal drug laws with legalization laws passed in Colorado and Washington, the DOJ issued a memo spelling out guidelines that must be met in order for the feds to permit states to legalize. These stipulations include having "strong and effective regulatory and enforcement systems to control the cultivation, distribution, sale, and possession of marijuana."

Grosso's bill would have provided that regulatory framework to go along with legalization. But Congress effectively made it impossible for the city to establish "regulatory and enforcement systems" by barring the use of federal funds to do so. Which means it is conceivable that DC could become the only place in the country with legalized marijuana — and essentially no rules surrounding the distribution or taxation of it.

DC's Mayor-elect Muriel Bowser signaled that she may allow DC to become an unregulated weed haven if that means protecting the right of DC to self-govern. Bowser previously said she would not consider any legalization law without a companion bill addressing the regulation and taxation of marijuana sales and distribution. But on Wednesday, she reportedly switched her position to support legalized and unregulated pot in the District.

"My job is to uphold the will of the voters, and the voters overwhelmingly support legalizing marijuana in the District," she said, according to the Washington Post.

The chairman of DC's council, Phil Mendelson, indicated that he will go ahead with bringing Initiative 71 to Congress for approval in January, which would begin a 30-day approval process. Following that, both the House and Senate would need to pass stand-alone measures specifically overturning legalization in the District to stop it from happening — and that's very unlikely.

"Getting the necessary votes in Congress to overcome this explicitly is going to be hard," John Hudak, a federal legal expert and fellow at the Brookings Institute, told VICE News. "There's not enough support in either party for that to happen. Democrats tend to support legalization more than Republicans, but there are a lot of Republicans that don't think this is the federal government's business."

"This is also not a fight John Boehner wants to have."

Grosso agrees, and pointed out that there have been only three Congressional overrides of DC laws in the past 40 years. Even more importantly, any Congressional measure blocking legalization in DC would require the signature of President Barack Obama, who has been a vocal supporter of DC's right to legalize marijuana and is unlikely to sign off on a law explicitly targeting legalization in the district.

"My guess is that [Congress] would have a very difficult time passing a resolution of disapproval because it would no longer be attached to the shut-down of the US government," Grosso said.

Adam Eidinger, who led the campaign to put legalization on the ballot in November, also sees marijuana remaining legal in DC.

"Less than an ounce of marijuana seeds will be legal to possess and share in the city, as long as you don't charge for it," he said today on local DC radio.

Congress could revoke the moratorium on taxing and regulating marijuana in DC through other means, such as rescinding the rider in a spending bill next year. But until that happens, it is likely that in DC, weed will be subject to fewer regulations than cigarettes.

Follow Olivia Becker on Twitter: @obecker928