The council supports Ross' bill because it lined up with its bylaw, and because it was concerned about washers' safety and the intimidation of drivers.
Window washers have been involved in several violent episodes.
In May last year, a 17 year-old washer attacked a driver with his cleaning brush at the Greenlane intersection - a popular spot for window washing. In July, three young window washers were arrested for robbery, also in Greenlane.
And in the most serious case, in April, a person who had been washing car windows beat a man who already had a brain injury with a copper pipe.
Green Party transport spokeswoman Julie Anne Genter asked the council why the law change was needed given that robbery and assault were already criminal offences. She also noted that the council's bylaw had failed to reduce window-washer related problems.
Filipaina said a law change would send a clear message to window washers about the dangers of their work.
National, Labour, Act and United Future supported the bill at the first reading. New Zealand First, the Green Party and the Maori Party voted against it.
The Greens said it would penalise poor people who were desperate to earn a few dollars.