Attorney General Jeff Sessions has rescinded an Obama-era policy that allowed legal marijuana to flourish in states across the country.

In a memo Thursday, Sessions says federal prosecutors should decide on their own whether to devote resources to marijuana cases based on other demands in their districts. Sessions writes in the one-page memo that "prosecutors should follow the well-established principles that govern all federal prosecutions" by considering the seriousness of the crime and its impact on the community.

It is not immediately clear how the decision will impact sales of the drug, which are legal on the state level in eight states and Washington, D.C.

But, as Sessions notes in the memo, marijuana remains federally illegal. Justice Department officials say they could take further action against states that have legalized pot but stopped short of offering specifics.

A Republican senator from Colorado is reacting angrily to Sessions' change to the federal policy affecting states that have legalized marijuana.

Cory Gardner says in a tweet that the Justice Department "has trampled on the will of the voters" in Colorado and other states.

Gardner said this contradicts what Sessions had told him before the attorney general was confirmed.

He said he was prepared "to take all steps necessary," including holding up the confirmation of Justice Department nominees, "until the Attorney General lives up to the commitment he made to me prior to his confirmation."