Most observers of marijuana policy are aware of the annual budget rider that has protected state medical cannabis laws from federal interference since late 2014. But many incorrectly assume that it is the only federal provision that makes an exemption for state-legal marijuana.

Actually, there is another, much more obscure U.S. regulation that carves out a manner of legitimacy and protection for cannabis activity that is legal under state law.

And, it’s 45 years old.

Enacted just two years after the founding of the National Organization for the Reform of Marijuana laws, the 1972 Federal Aviation Administration (FAA) rule banning pilots from operating aircraft with illegal substances on board specifies that it “does not apply to any carriage of narcotic drugs, marihuana, and depressant or stimulant drugs or substances authorized by or under any Federal or State statute or by any Federal or State agency.” [Bolded emphasis added.]

An earlier, 1969 version of the regulation did not contain the clause protecting state-legal activity.

It is unclear what occurred during the three-year window between the versions that prompted FAA to make exemptions for state marijuana laws, but the 1972 revision does contain explanatory text showing that the penalty-setting provision preceding the clause with the state exceptions was also amended. Previously, it, too, only concerned federal laws and violations thereof.

“Since the adoption of Amendment 91-66, information available to the FAA indicates that the illicit carriage of drugs by aircraft may be occurring in various places within the United States and involve violations of State as well as Federal statutes,” the agency wrote in the Federal Register. “Accordingly, in order to cope effectively with the threat to safety in air commerce from such illicit carriage of drugs, it is proposed to amend § 91.12(a) and make the prohibition therein apply to the operation of civil aircraft within the United States with knowledge that narcotic drugs, marihuana, and depressant or stimulant drugs or substances as defined in Federal or State statutes are carried in the aircraft.”

When it comes to the subsequent exemption clause, it is remarkable that the federal government may have contemplated as far back as 1972 not only that states would begin legalizing marijuana but that activity in accordance with those laws should be shielded from a federal penalty on airplane pilots.

It wasn’t until 24 years later, in 1996, when California became the first state to enact a broad medical cannabis policy, and full-scale adult-use legalization didn’t arrive until Colorado and Washington State ended their prohibition laws in 2012. (Beginning in 1978, a number of states enacted mostly symbolic and ineffective medical marijuana laws that didn’t provide patient access, but that was still six years after the FAA rule change.)

While it is possible that FAA didn’t actually mean in 1972 to protect consumers carrying future-legal cannabis in the sky — and may have just meant to make sure law enforcement could legally transport seized contraband — a plain reading of the regulation would seem to have that perhaps unintended effect today.

In any case, it is still on the books. And very few people working on cannabis issues, if any, seem to have ever noticed it.

None of a half-dozen longtime D.C.-based marijuana policy reform advocates that Marijuana Moment reached out to for this story said they were aware of the FAA exemption’s existence.

But the provision could nonetheless have huge implications for the growing number of states that are making marijuana legal for medical or recreational purposes.

Much has been made, for example, of licensed cannabis producers’ difficulties in transporting their wares in states with populated islands.

A 2014 Seattle Times story on legal cannabis access by Washington State residents living on islands mentions the FAA’s ban on using aircraft to transport illegal drugs, but makes no mention of the decades-old exemption for state-legal marijuana products.

A 2015 Martha’s Vineyard Times piece describes difficulties in getting Massachusetts-legal cannabis to the island and raises federal concerns, but it, too, ignores the FAA exemptions for state laws.

While crafting medical cannabis regulations, Hawaiian legislators included their own state-level prohibition on interisland transportation. A lawmaker indicated in a 2016 Associated Press interview that she and colleagues were “trying to figure out how to get around federal laws that prevent marijuana from being transported by sea or air,” according to the news organization’s paraphrase of her remarks.

And earlier this year, a Boston Globe story even linked to the relevant section of FAA regulations to cite the ban, but the reporter apparently didn’t notice the state carve-out in the following clause.

States could potentially be able to solve their local transport issues by citing the little-known exemption. But, depending on the Trump administration’s response, the issue could end up being settled by courts.

And while the provision in question only concerns the ability to operate aircraft and doesn’t directly implicate broader interstate drug trafficking issues under the Controlled Substances Act, the fact that the exception exists could provide some room for arguments about Transportation Security Administration policies on the transport of marijuana on commercial planes, for example, as well as other gray areas at the intersection of conflicting federal and state drug laws.

After this story was published, a reader pointed out that Marijuana Business Daily briefly discussed the FAA regulation’s state-legal exemption in an earlier piece about transportation issues.