Fonda and Tomlin played Judy Bernly and Violet Newstead in 9 to 5, with Parton as Doralee Rhodes. The pair told host Ellen DeGeneres they are "trying" to get the sequel made.
"We're trying," Fonda said. "We've got people writing it, hopefully."
Fonda said she initially met Tomlin a year or two before they worked on 9 to 5. She saw Tomlin perform in the play Appearing Nightly and was "gobsmacked" by the actress' talent.
"I totally changed the idea for 9 to 5 because of her. Because I said, 'I don't want to make a movie about secretaries if she's not in it,'" the star recalled.
Fonda, who came up for the idea for the the film, said she found Tomlin before seeking out Parton.
"It was Lily. And then driving home from seeing her, I turned the radio on and Dolly was singing. I thought, 'Oh, wouldn't that be interesting. You know, typing and she can't see her fingers?'" she joked.
Fonda previously said at a Television Critics Association panel in July that she, Tomlin and Parton are "intending" to be in the sequel.
"My role is as an executive producer, and I'm working with the writers, with Lily, and talking to the writers," she said.
Fonda and Tomlin star in the Netflix series Grace and Frankie, which will return for a fifth season Friday.