Birds of Prey star Margot Robbie fought an "uphill battle" while pitching the film.
The 29-year-old actress said in the January digital issue of Glamour U.K. that she struggled to get a green light for the female-led project.
Robbie played the DC Comics character Harley Quinn in the 2016 movie Suicide Squad and approached Warner Bros. about a followup film based on the female superhero team Birds of Prey.
"It was an uphill battle. I pitched it four years ago," Robbie said.
"I pitched it with a deck I made," she shared. "It was pretty thick. It had comps of other female ensemble action films that had done well and ones that didn't do well and my theory as to why and what we could do. But really, I was just saying we need to do a female ensemble action film. I don't know why where aren't more of them."
In addition to the female-led concept, Robbie pitched the movie as being rated R.
"I wanted it to be R rated so we didn't feel restricted in the language or the violence, because if it was a PG rating, guys can feel like it's a 'chick flick,'" she explained.
Birds of Prey is directed by Cathy Yan and co-stars Mary Elizabeth Winstead, Jurnee Smollett-Bell and Rosie Perez. Warner Bros. shared a poster for the film in September featuring Robbie as Quinn.
Robbie, who launched her own production company, LuckyChap Entertainment, in 2014, told Glamour U.K. she's fought an uphill battle as a producer. The actress said she's experienced sexism, often in the subconscious undertones of interactions.
"It's naturally ingrained in people -- even if you are the one who should be dictating the decisions -- that they turn to the closest, eldest male in the room and direct the question at them. It's just an inherent thing everyone has got in their DNA," Robbie said.
"When people are asking a question and I have the answer, they so readily will turn to my producing partners who are guys and ask them," she added. "It's the societal construct we have grown up knowing."
Birds of Prey opens in theaters Feb. 7. Robbie will also return as the voice of Flopsy Rabbit in Peter Rabbit 2: The Runaway, which released a first official trailer Wednesday
