President Joe Biden took steps to overhaul U.S. policy on marijuana on Thursday by pardoning thousands of people with federal offenses for simple marijuana possession and initiating a review of how the drug is classified.

Biden said thousands of people with prior federal convictions could be denied employment, housing or educational opportunities and his executive action would relieve such "collateral" consequences.

Nearly 40 U.S. states have legalized marijuana use in some form, but it remains completely illegal in some states and at the federal level. Reclassification would be the first step toward wider legalization, a move backed by a majority of Americans, and usher in sweeping changes for companies and law enforcement and impact millions.

The president's decision fulfills a campaign promise and is likely to please members of his left-leaning political base ahead of the November midterm elections in which the president's fellow Democrats are defending control of the House of Representatives and Senate.

"Too many lives have been upended because of our failed approach to marijuana. It's time that we right these wrongs," Biden said.

He urged state governors to follow suit.

"Just as no one should be in a federal prison solely due to the possession of marijuana, no one should be in a local jail or state prison for that reason, either," Biden said.

A senior administration official said more than 6,500 people with prior federal convictions could be affected by the pardons.

Supporters welcomed the move and its impact on racial imbalances in the U.S. justice system.

Some Republicans, who U.S. voters prefer over Democrats for addressing crime-related policies, criticized it.

"In the midst of a crime wave and on the brink of a recession, Joe Biden is giving blanket pardons to drug offenders — many of whom pled down from more serious charges," Republican Senator Tom Cotton said on Twitter.