In a magazine interview, Portman revealed that she was paid three times less than her male co-star Ashton Kutcher for her role in the 2011 romantic comedy "No Strings Attached".
"Compared to men, in most professions, women make 80 cents to the dollar," Portman told Marie Claire. "In Hollywood we are making 30 cents to the dollar."
The 35-year-old star - who won a best actress Oscar in 2011 for her role in "Black Swan" and plays Jackie Kennedy in a forthcoming biopic about the former U.S. First Lady - said the pay disparity was "crazy".
The World Economic Forum, a non-profit foundation, predicts the global gender pay disparity may take up to 170 years to close. The average global gap stood at 59 percent in 2016, it said in a report released last October.
Hollywoods gender pay gap was highlighted in 2015, when hacked documents from film studio Sony Pictures revealed major pay disparities between top actors.
They showed that U.S. actress Jennifer Lawrence was paid less than her male co-stars Christian Bale and Bradley Cooper in the 2013 black comedy "American Hustle".
Hacked emails showed that Bale and Cooper earned nine percent of the films total profits, whilst Lawrence was only paid seven percent.
Lawrence later said she was "mad at herself" after learning about the pay gap because she had "failed as a negotiator".
Other movie stars - such as Sandra Bullock and Jessica Chastain - have also hit out at pay discrimination.
The 2017 awards season began on Sunday with the Golden Globes dinner in Beverly Hills, kicking off two months of red carpets and black tie events, culminating in the Academy Awards ceremony on Feb. 26.
Actress Meryl Streep turned her Golden Globe acceptance speech into a scathing commentary on U.S. President-elect Donald Trump, stunning her audience into silence and grabbing headlines with her criticism of Trumps impersonation of a disabled newspaper reporter.
Last year, the Academy Awards were heavily criticised for picking an all-white lineup of best actor nominees, prompting boycotts from several big names, including Will Smith, Jada Pinkett-Smith and Spike Lee.
The criticism became widely associated with the Twitter hashtag #OscarsSoWhite.