The development comes after a report, originally published by The Washington Post, and later by USA Today, claims Wahlberg earned USD 1.5 million, while Williams made less than USD 1,000.
According to Variety, a spokesperson for SAG-AFTRA, which is the union representing both the actors, said that the organisation is looking at the circumstances of the pay disparity.
"We are unambiguously in favor of pay equity between men and women in this industry and support every action to move in this direction.
The film made the headlines last year when Scott decided to reshoot Kevin Spacey's scenes following allegations of sexual harassment against the actor.
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Christopher Plummer was roped in to replace Spacey and the veteran actor reshot the scenes barely six weeks before the film's scheduled release.
Scott told USA Today in December that "everyone did it for nothing".
The report about the glaring pay disparity has gone viral on social media and invited criticism by many celebrities, such as Jessica Chastain, Mia Farrow and Judd Apatow.
Getty Sr famously negotiated the ransom.