Union weighs in on reported wage gap between Mark Wahlberg and Michelle Williams

— -- The actors union SAG-AFTRA has responded to a report that Mark Wahlberg was paid $1.5 million for the reshoot of "All the Money in the World," while his co-star Michelle Williams received an $80 per diem, totaling less than $1,000.

A union spokesperson told ABC News in a statement, "We are unambiguously in favor of pay equity between men and women in this industry and support every action to move in this direction. At the same time, performers at this level negotiate their above-scale rates through their agents."

The statement added, "As it relates to this matter, you should talk to their representatives."

Publicists for Wahlberg and Williams did not respond to requests for comment. A source close to the production told ABC News that Sony, the film's distributor, had nothing to do with funding or pay negotiations.

The report on the massive wage disparity -- which amounts to Williams receiving less than 1 percent of her male co-star's fee -- was first published in USA Today.

The film about the 1973 kidnapping of billionaire J. Paul Getty's grandson originally cast Kevin Spacey in the role of Getty. After Spacey faced a cascade of sexual assault allegations, director Ridley Scott recut the film with actor Christopher Plummer less than two months before its scheduled release.

Last December Williams told ABC News that she was all in favor of the reshoots because she didn't want the film to be tainted by the Spacey scandal. She even declined to be paid an additional salary.

"I received a phone call from a producer and [they] said, ‘Please don’t talk to anybody about this, but would you, if we could?’ And I said, ‘Not only would I, but I’ll give you back my salary if that would help. And I’ll give you my Thanksgiving break, if that would help.’ And they, to their credit, they only took my Thanksgiving break," Williams said.

In December, Scott told USA Today that all the actors, minus Plummer, "came in free" and agreed to work for nothing.

But on Tuesday, USA Today reported that Wahlberg’s team negotiated his $1.5 million fee for the reshoot, and Williams, who is represented by the same agency, was not told about it.

Celebrities took to Twitter to voice their outrage about the pay disparity and express their support for Williams following Tuesday's report.

Among those speaking out was Williams good friend, actress Busy Phillips.

"UNACCEPTABLE. UNACCEPTABLE!!!!!!!!!!!!!!!!!!!!! TO SAY THE LEAST," she tweeted.

Jessica Chastain, an outspoken advocate of gender parity for Hollywood salaries, wrote in support of Williams, "She has been in the industry for 20 yrs. She deserves more than 1% of her male costar's salary."

Jesse Tyler Ferguson was "furious."

Tamblyn called the report "unacceptable."