Devyn LaBella filed the lawsuit in Los Angeles Superior Court. It names Costner - the director, star and co-writer of the Horizon series of Westerns - and its production companies as defendants.
"The impact of this impromptu work demand on Ms LaBella has been profound, not only upending a career Ms LaBella spent years building but leaving her with permanent trauma that she will be required to address for years to come," the lawsuit says.
Costner's lawyer said the lawsuit has no merit, and LaBella's assertions are contradicted by both the facts and her behaviour.
A former gymnast, the 34-year-old LaBella has worked steadily as a Hollywood stunt performer since 2020, with credits including Barbie and Yellowjackets.
LaBella's lawsuit says she was the stunt double for one of the Horizon leads, Ella Hunt, throughout the production.
The shoot included a planned sexual assault scene, shot in May of 2023, that LaBella performed much of because of its violent and physical nature, the lawsuit says. For that scene, protocols were followed, including meetings, rehearsals, the presence of an intimacy coordinator and minimal crew.
But it alleges that the following day, in an unscripted scene with no warning, rehearsal or choreography, Costner directed an actor to pin LaBella down on a wagon and simulate rape. The lawsuit says Costner asked for many takes as he experimented with the violent action and did not make it clear when a shot was beginning or ending.
"There was no escaping the situation, and all Ms LaBella could do was wait for the nightmare to end," the suit says.
It alleges that safeguards were ignored in violation of union contracts and industry standards.
Costner's lawyer, Martin Singer, said while the Hollywood actor wants everyone to be comfortable on his sets, LaBella's claim has "absolutely no merit, and it is completely contradicted by her own actions - and the facts."
"The scene in question was explained to Ms LaBella, and after she performed the rehearsal in character with another actor, she gave her stunt co-ordinator supervisor a 'thumbs up' and indicated her willingness to then shoot the scene, if needed (which she was not)," Singer said in a statement.
"That night, Ms LaBella had dinner with her supervisor, the stunt coordinator, and with the assistant stunt coordinator, and she was in good spirits and made no complaints to them. She continued to work on the movie for a few more weeks until her wrap date, and she took the stunt co-ordinator to a thank-you dinner."
Singer provided an image of a text message LaBella sent her stunt coordinator at the end of production saying, "Thank you for these wonderful weeks!"
Singer said LaBella "is a serial accuser of people in the entertainment industry."
The Associated Press does not typically name people who say they have been sexually abused unless they come forward publicly, as LaBella has done.
The lawsuit seeks damages in an amount to be determined at trial, and it seeks a judge's order for the defendants to undergo sexual harassment training, to be required to use an intimacy co-ordinator on future productions and to issue LaBella a public apology.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
Lifeline 13 11 14
Men's Referral Service 1300 766 491
