An apparent error in the $1.1 trillion spending bill approved by Congress on Thursday deprives two states with medical marijuana laws of protection against federal anti-drug agents and prosecutors.

The bill awaits President Donald Trump's signature after winning Senate approval and will dictate the use of federal funds through September.

For unknown reasons, medical pot programs in North Dakota and Indiana were not listed as being off-limits to federal enforcement in the bill, which was negotiated by congressional leaders before being presented for floor votes.

The omission, first reported on Massroots.com Monday by journalist and activist Tom Angell, is sparking concern about a loophole that could be exploited by Attorney General Jeff Sessions, an opponent of marijuana use and a skeptic about its medical value.

"I think it is concerning that North Dakota’s brand-new law might be treated differently as a result of this," says Tim Purdon, who served as U.S. attorney for North Dakota from 2010 to 2015.

"You just hope DOJ and folks wouldn't take advantage of what appears to be a mistake or some kind of loophole," Purdon says.

North Dakota voters in November approved a medical pot initiative, alongside voters in Arkansas and Florida. Indiana's governor last week signed legislation creating a registry for state-legal use of the cannabis compound cannabidiol (CBD).

Through earlier versions of the amendment, federal spending bills have since 2014 banned the Justice Department and its subsidiaries from targeting state-legal medical marijuana programs. The shield, known as the Rohrabacher-Farr amendment, is a foundational legal measure for the national cannabis industry.

Federal courts have found the measure protects state-legal medical marijuana enterprise, even though cannabis possession remains a federal crime.

Forty-four states, the nation's capital, Guam and Puerto Rico are named in the latest edition of the amendment.

Idaho, Kansas, Nebraska and South Dakota are the other states not named as protected.

"We don't know" why the two states were omitted, says Ken Grubbs, communications director for Rep. Dana Rohrabacher, R-Calif., one of the measure's chief champions and its namesake.

"It could have been inadvertent, evidence that the legalization movement is so fluid members couldn't keep up," Grubbs says.

Grubbs says the measure was not revised before passage, and an employee of the House appropriations committee identified the final bill as a document that contains the omission.

State and federal officials reached by U.S. News either declined to comment or said they were reviewing the spending bill.

A spokeswoman for the North Dakota attorney general's office referred questions to the office of the U.S. attorney for North Dakota, which was not immediately able to comment.

The Indiana attorney general's office says it is reviewing the matter. A spokesman for the U.S. attorney's office in southern Indiana did not immediately respond to an inquiry, and a spokesman for the northern Indiana office referred questions to the Justice Department press office.

"We will review the legislation and decline to comment further at this time," Justice Department spokesman Peter Carr says.

More than half of states currently have medical marijuana laws. Eight states, meanwhile, have laws authorizing the regulated sale of recreational marijuana.

Though it initially presided over a controversial medical marijuana crackdown, the Obama Justice Department in 2013 issued the so-called Cole Memo, which allows states broad leeway over cannabis regulation as a matter of policy.

Sessions has ordered a review of federal marijuana policy, with a committee of unknown membership expected to issue recommendations in coming months.