The 47-year-old actress signed onto "Lovelace", about the porn icon who starred in 1972's "Deep Throat", last year after Demi Moore dropped out from the film due to health problems, reported Daily Star online.
The drama, which stars Seyfried as the titular character, is set to premiere at the Sundance Film Festival in Utah next week, but viewers won't get to see Parker's performance - since filmmakers decided to end Lovelace's story in 1980, four years before she met Steinem.
And director Rob Epstein said that it was a tough decision to leave Parker's scenes on the editing room floor.
"You never want to make that call," he said.