Construction workers facing legal action for downing tools several hours before a rally in Perth say it's an outrageous attack on workers' rights and civil liberties.

The Fair Work Building Commission (FWBC) is serving summonses on 76 Crown Construction workers who attended a rally calling for more local jobs and content in Western Australia’s mining sector on February 28 last year.

Each of the workers face a fine of $10,200.

The FWBC alleges some of the workers constructing the new Children’s Hospital in Nedlands either left the site, did not show up at all or refused to perform any work from 7.30am (WST).

The rally was held around midday (WST).

The FWBC claims this constituted industrial action, which breached a Fair Work Commission order issued only nine days earlier.

“It is simply the government going after ordinary workers for daring to take a stand on the issue of local jobs and better opportunities for their kids,” said CFMEU Construction secretary Dave Noonan, who was one of the speakers at the rally.

“Workers in Australia should be able to participate in a peaceful political protest without the threat of being dragged before the courts by the government.”

A directions hearing is scheduled for March 28.