President Obama on Thursday commuted the prison sentences of eight inmates serving time for crack cocaine offenses, part of a major push by the White House to alleviate so-called mandatory minimums for nonviolent drug crimes.

Prior to Thursday, Obama had commuted just one sentence, wielding the presidential power far less than his predecessors

“Today, I am commuting the prison terms of eight men and women who were sentenced under an unfair system,” Obama said. “Each of them has served more than 15 years in prison. In several cases, the sentencing judges expressed frustration that the law at the time did not allow them to issue punishments that more appropriately fit the crime.”

Although Obama three years ago signed the Fair Sentencing Act — which reduced penalties for crack cocaine offenses —the law applied only to new cases.

The Justice Department has also launched an effort to crack down on the disparity in sentences for nonviolent drug crimes, saying minorities are disproportionately imprisoned at a great cost to taxpayers.

“If they had been sentenced under the current law, many of them would have already served their time and paid their debt to society,” Obama said of the commutations.

Obama granted clemency to a total of 21 people, including 13 pardons to people who had already completed their prison terms.

Obama had previously pardoned just 39 people.

Advocates for more flexible prison sentencing cheered the president’s announcement.

“President Obama today gave several Americans who were unnecessarily sentenced to die behind bars the chance to reunite with their families,” said Vanita Gupta, deputy legal director of the American Civil Liberties Union. “This is one important step toward undoing the damage that extreme sentencing has done to so many in our criminal justice system.”

Obama also called on lawmakers to “act on the kinds of bipartisan sentencing reform measures already working their way through Congress.”

However, some conservatives have balked at such bills, arguing they amount to soft-on-crime policies that would make communities less safe.