Legal proceedings have been launched against 76 workers who allegedly took unlawful industrial action at the new Perth Children's Hospital.

Fair Work Building and Construction (FWBC) alleges employees of a subcontractor on the $1.2 billion project ignored an order by the Fair Work Commission not to take industrial action.

FWBC claims that on February 28, 2013, the 76 employees left work, did not come into work or refused to do work while on site.

FWBC alleges employees were in breach of the Fair Work Act by engaging in industrial action before the enterprise bargaining agreement expired, and breached the terms of an order issued by the Fair Work Commission not to engage in industrial action.

A directions hearing is scheduled for March 28.  The maximum penalty for each breach of the act is $10,200 for an individual.

FWBC alleges each employee breached two sections of the act.