Polanski was arrested in Switzerland last month (Sep09) and faces a return to Los Angeles courts to face sentencing for the 1977 assault of a 13-year-old girl.
The victim, Samantha Geimer, has begged the authorities to drop the case and let Polanski walk free, claiming the fuss over the director's detention has caused problems for her and her family, and turned her into a news target.
But top lawmakers, led by State Senator Gloria Romero, insist a sentencing trial must take place so a statement about the seriousness of domestic violence can be made.
Romero and her peers have praised Los Angeles County District Attorney Steve Cooley for pursuing the case.
In the open letter, the legislators write, "Like any other person, he should be returned to face sentencing as well as face his past. Anything short of this undermines a fundamental premise that justice is blind and no one is above the law.
"Despite the debates about Mr. Polanski's extradition, I am struck by how magnanimous his victim was by her forgiveness of his crime against her and, certainly, her words will carry weight in a court of law. But, nonetheless, closure is expected and needed."