The CFMEU and seven of its senior officials have been handed hefty fines for three contraventions of the Fair Work Act at the site of the new Perth Children's Hospital.
The union and officials, including WA state secretary Mick Buchan and assistant state secretary Joe McDonald, were fined a total of $277,000 in the Federal Court on Thursday.
The first offence was a blockade and strike on January 25 and 30, 2013 when officials stood at the front gate and directed workers to attend a safety meeting nearby.
The Australian Building and Construction Commission said between 109 and 136 employees were unable to work on the first day because they were either prevented from entering the site or dissuaded from doing so.
On the second date, Tawa Harris physically blocked the entrance and tried to prevent employees from entering the site, delaying work by 45 minutes, despite the Fair Work Commission having just days earlier issued orders to prevent industrial action on the project.
The second offence was on May 3 that same year, when another blockade and strike prevented 207 workers from being on site.
The commission said the third offence on July 18, 2013 was the most serious, involving "an elaborate plan" to arrange a vast crowd at the site, with numbers surging to 400 people at one point.
A massive concrete pour planned for that day had to be abandoned and 205 employees did not work that day.
The protest was organised because the head contractor John Holland refused a demand for a "whole-of-site" enterprise bargaining agreement.
Mr Buchan said industrial laws had become unbalanced and favoured employers over employees.
"These workers were rightly concerned about the race to the bottom that predatory contracting practices on the site had started," he said.
"We held a rally to discuss that and other concerns bubbling up from the workforce."