Labor figures linked to Bill Shorten behaved "more like schoolboys" than men when they vandalised rival parties' placards on election day, a magistrate said on Friday, before fining each $1000.

Shorten confidant Andrew Landeryou, David Boutros-Asmar, George Droutsas and Dean Sherriff were charged with five counts of damaging and five counts of stealing rival Liberal and Greens campaign advertising material on July 2 last year. Mr Sheriff was also charged with assault.

Andrew Landeryou is a confidant of Labor leader Bill Shorten. Credit:Arsineh Houspian

The acts of vandalism took place at polling booths at Elwood, St Kilda, Albert Park, Port Melbourne and Middle Park.

Magistrate Ann Collins described their actions as "one stupid mistake" and told them on Friday they should respect the right to freedom of expression and the rule of law.