WASHINGTON — The viability of the multibillion-dollar marijuana legalization movement was thrown into new doubt on Thursday when the Trump administration freed prosecutors to more aggressively enforce federal laws against the drug in states that have decriminalized its production and sale, most recently California.

Attorney General Jeff Sessions, long a vocal opponent of the legalization of marijuana, rescinded an Obama-era policy that discouraged federal prosecutors in most cases from bringing charges wherever the drug is legal under state laws.

“It is the mission of the Department of Justice to enforce the laws of the United States, and the previous issuance of guidance undermines the rule of law,” he said in a statement. In his memo to United States attorneys, he called the earlier policy “unnecessary” and pointed to federal laws that “reflect Congress’s determination that marijuana is a dangerous drug and that marijuana activity is a serious crime.”

Democrats and some Republicans condemned the move. Senator Cory Gardner, Republican of Colorado, threatened to retaliate by holding up Justice Department appointments that required Senate approval. Gavin Newsom, the Democratic lieutenant governor of California, vowed to encourage cooperation among states that have legalized marijuana.