Andrea Riseborough will keep her controversial Oscar nomination for "To Leslie" even though a review of the indie film's unorthodox promotional campaign uncovered concerns, the Academy said Tuesday.

The British star's best actress nomination, unveiled last week by Hollywood's most prestigious awards group, sent shockwaves through the industry.

While her performance was lauded by critics, the film had grossed just $27,000 at the box office, and had not received the sort of expensive and highly visible marketing campaign that is widely seen as essential for Academy Awards glory.

The movie -- about a Texas mother who won the lottery but squandered her fortune and descended into alcoholism -- instead relied upon an intense, last-minute social media campaign mounted by prominent celebrities including Edward Norton, Gwyneth Paltrow and Sarah Paulson.

Debate has raged in Hollywood over whether any Academy rules against lobbying or disparaging rivals were broken.

"The Academy has determined the activity in question does not rise to the level that the film's nomination should be rescinded," the Oscar-awarding group said in a statement Tuesday.

"However, we did discover social media and outreach campaigning tactics that caused concern. These tactics are being addressed with the responsible parties directly."

The Oscars are awarded based on the votes of the 9,500 members of the Academy of Motion Picture Arts and Sciences.

Nominations are determined by each Academy branch, meaning the Oscar nominations for actors including Riseborough were voted on by around 1,300 actor members of the group.

It is these members who were allegedly targeted with e-mails and social media posts, encouraging them to vote for Riseborough and ask others to do so.

At least one Instagram post supporting "To Leslie" suggested that Riseborough's rivals such as Danielle Deadwyler and Viola Davis were "getting nominated anyway," so members' votes could safely be directed elsewhere.

Neither Deadwyler nor Davis -- who are both Black -- ended up receiving nominations. No Black stars received lead actress nods this year.

"The purpose of the Academy's campaign regulations is to ensure a fair and ethical awards process -- these are core values of the Academy," said the Academy statement.

The review made it clear that "components of the regulations must be clarified to help create a better framework for respectful, inclusive, and unbiased campaigning."

Any changes will not be made until after this year's Oscars ceremony, which take place on March 12.

"The Academy strives to create an environment where votes are based solely on the artistic and technical merits of the eligible films and achievements," the statement concluded.