She said at a Wednesday news conference with her date that she needed the money to pay her bills and to support her grandchildren.
"I support a lot of people," Fonda said.
Jane Fonda is going on a date with 90-year-old Richard Lugner, pictured here, because he’s paying her. (AP Images)
She acknowledged not being well-informed about the event before she accepted Lugner's invitation, telling reporters she thought it was to an "opera performance" and not a ball.
Fonda, who is well known for her activism to curb climate change, said she was "sorry" to learn Austrian oil and gas company OMV sponsored the Vienna Opera Ball.
"These fossil fuel companies are criminal. They’re criminal. They’re killing people. They’re killing the planet," the "Grace and Frankie" star remarked.
"Please try to get your opera to stop taking support from an oil company," she added.
Jane Fonda cites "a fake shoulder, two fake hips, and two fake knees" as the reason she won't be dancing at the ball. (AP Images)
The 85-year-old joins the list of female celebrities that have cozied up next to Lugner, as he’s known for paying undisclosed sums of money to famous women to be his date to the ball.
JANE FONDA REVEALS CANCER DIAGNOSIS: THIS IS 'VERY TREATABLE'
Notable guests, including Pamela Anderson, Kim Kardashian and model Elle MacPherson were among the stars who shared an evening with Lugner at the Vienna Opera Ball.
Fonda said her commitment would not include dancing at the ball because she has a "fake shoulder, two fake hips, two fake knees.
"I’m old, and I may fall apart," said the actor.
Jane Fonda stars in '80 for Brady' with Sally Field, Rita Moreno, Lily Tomlin, Tom Brady and more. (Jon Kopaloff/Getty Images)
Celebrity Net Worth estimates that Fonda is worth $200 million. According to the website, her money comes from her family and her extensive career.
Fonda is the daughter of famed actor Henry Fonda and socialite Frances Seymour Brokaw.
Since "80 for Brady" movie release, the comedy-drama brought in a higher-than-expected take of $12.5 million and locked in the number two spot at the box office in its opening weekend, according to the New York Times.
Jane Fonda plans to use the money from Lugner to support her family. (Emma McIntyre)
The "Book Club" actress recently said that when she met former NFL star Tom Brady, her knees grew weak from being starstruck.
"Tom Brady, I think he went into all of our trailers individually," she recalled during a Q&A, according to Variety. "And when he walked into my trailer at the end, my knees gave way."
The Associated Press contributed to this report.