SALEM, Ore. — When U.S. Attorney General Jeff Sessions green-lighted federal prosecutions of marijuana lawbreakers, the vast majority of U.S. states that allow some form of medical marijuana were unexpectedly placed at risk of a crackdown and are warily watching developments.

Forty six states — including Sessions’ home state of Alabama — have legalized some form of medical marijuana in recent years, according to the National Conference of State Legislatures. Eight of those states also allow recreational marijuana.

Among the guidance that Sessions rescinded was the so-called Ogden Memorandum of 2009 that instructed federal prosecutors not to pursue cases against medical marijuana patients and distributors who complied with state laws.

“Previous nationwide guidance specific to marijuana enforcement is unnecessary and is rescinded, effective immediately,” Sessions told the U.S. attorneys based in all 50 states in a letter Thursday.

Georgia state Rep. Allen Peake, a Republican who sponsored a bill in his state’s legislature that legalized possession of medical marijuana in 2015, denounced the move.

“I’m very disappointed in Jeff Sessions’ actions,” Peake said Friday in a telephone interview. “He will be hurting the grandfather with Alzheimer’s, the soccer mom with breast cancer, the college student with Crohn’s disease, the young child with seizures — these are the people that will be impacted by this action by the attorney general.”

The only legal protection now for medical marijuana growers, processors, sellers and users is a temporary measure sponsored by Rep. Dana Rohrabacher, R-Calif., and Rep. Earl Blumenauer, D-Ore., prohibiting the U.S. Department of Justice from using government funds to target them.

Rohrabacher, in a conference call with reporters and four other members of Congress, said Sessions’ move should galvanize national support for marijuana legalization.

“This is a wakeup call for American people who believe in freedom,” Rohrabacher said. “It will mobilize people throughout the country.”

Many politicians, including Republicans, have cast Sessions’ move as an infringement on states’ rights.

Only Idaho, South Dakota, Nebraska and Kansas do not allow any access to marijuana, said Karmen Hanson, a cannabis policy analyst with the National Conference of State Legislatures. Twenty nine states — plus Washington, D.C. and the U.S. territories of Guam and Puerto Rico — allow for comprehensive public medical marijuana programs. An additional 17 states allow use of marijuana products for medical reasons in limited situations or as a legal defense, she said.

Many of the states that allow some form of medical marijuana did so in 2013 and 2014. About half of the initiatives have been passed by voters in ballot measures, and the rest by state legislatures, Hanson said.

Georgia’s General Assembly passed that state’s medical marijuana law in 2015. Called Haleigh’s Hope Act, it was named for a girl who was suffering from hundreds of seizures a day.

“This means the world to us,” Haleigh’s mother, Janea Cox, told reporters when Georgia’s governor signed the bill.

Peake said Sessions’ move will have a chilling effect on a bill he introduced that would allow the growing, processing and distribution of cannabis oil in Georgia.

“This is as bipartisan an issue as you can get,” he said. “Cancer doesn’t ask if you’re a Republican or a Democrat. There are people of all races and creeds who benefit from medical cannabis, so that’s why it’s so crucial that Congress get together and take action.”

The Rohrabacher-Blumenauer Amendment that restricts U.S. attorneys from taking legal action against people who use medical marijuana or produce it was maintained in a last short-term funding bill passed by Congress. But that funding bill expires on Jan. 19.

Blumenauer “is working to make sure it’s maintained again in whatever next funding bill Congress passes,” said his spokeswoman, Nicole L’Esperance.

Rohrabacher said a better, more permanent solution is a bill he submitted last year that amends the Controlled Substances Act so it doesn’t apply to people who produce, possess or deliver marijuana in compliance with state laws.