LOS ANGELES – The Academy of Motion Picture Arts and Sciences, organizer of the Oscar awards, pledged on Friday to double its membership of women and minorities by 2020 through an ambitious affirmative action plan that includes stripping some older members of voting privileges.

The announcement came amid a backlash over the absence of actors or filmmakers of color in this year’s Oscars nominations, prompting actor Will Smith, director Spike Lee and a handful of others to say they plan to shun the Oscars ceremony on Thursday.

The membership rule changes, among the most sweeping in the academy’s 88-year-old history, were unanimously adopted by the organization’s Board of Governors on Thursday night, the group said in a statement. But the reforms will not affect voting for this year’s Academy Awards.

A lack of diversity within the academy, whose ranks consist mostly of older, white men, has long been cited as a barrier to racial inclusion in Hollywood’s highest honors.

But many critics point to the scarcity of opportunities for minorities and women on either side of the camera in a film industry that largely relegates them to marginal or stereotyped roles.

Academy President Cheryl Boone Isaacs, who became the first African-American to assume the organization’s top post in the summer of 2013, hailed Friday’s move as demonstrating the academy is ready “to lead and not wait for the industry to catch up.”

But Ava DuVernay, who became the first black filmmaker to earn a Golden Globe bid for her for Oscar-nominated civil rights drama “Selma” last year, said the academy’s action was a long time in coming and taken only under duress.

“Marginalized artists have advocated for Academy change for DECADES,” she wrote in a Twitter message, adding: “Actual campaigns. Calls voiced FROM THE STAGE. Deaf ears. Closed minds.”

As part of its new push to expand gender and racial diversity, the academy said it will add three new seats to its 51-member governing board reserved for women and minorities.

The academy said it also would augment its process by which current members sponsor newcomers to the organization by launching “an ambitious global campaign to identify and recruit qualified new members who represent greater diversity.”

“The board’s goal is to commit to doubling the number of women and diverse members of the academy by 2020,” the statement said.

Under new eligibility rules, each new member’s voting status will lapse after 10 years unless he or she has been active in motion pictures during that decade, and lifetime voting rights will only be conferred after three 10-year terms or if the member has won or been nominated for an Oscar.

The same standards will apply retroactively to current members, meaning those who have been inactive in film during the past 10 years would have to either be nominated for an Oscar or win one to qualify, the academy statement said.

Those losing eligibility to vote would be moved from active to “emeritus” status, absolving them of paying dues while leaving their academy privileges intact, except for voting.

“The academy has a geezer problem. There are a lot of old has-beens in their ranks,” said Tom O’Neil, editor of the awards-watching website Gold Derby. “It’s a very dramatic announcement and a very welcome breakthrough.”

How many new female or minority members the academy would need to enlist to meet its goal, and how many older members stand to lose their voting privileges was not immediately clear.

The roster of the 6,000 or so academy members has never been publicly disclosed, though a 2012 Los Angeles Times study found its members were nearly 94 percent white and 77 percent male.

The academy faces a mounting protest over a lack of racial minorities among this year’s nominees in its four acting categories for a second year in a row, and the failure of academy voters to nominate the critically acclaimed hip-hop drama “Straight Outta Compton” in this year’s contest for best picture.