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Tradies again down tools at Opera House

Workers tasked with the $200 million refurbishment of the Sydney Opera House have walked off the job for the second time after again reportedly being exposed to asbestos.

Electrical workers downed tools on Friday morning and refused to install cable through the iconic building after it was confirmed potentially deadly asbestos had been found, the Electrical Trades Union said in a statement.

Samples collected on Wednesday contained friable asbestos which can crumble into powder making it easier to inhale or ingest.

The discovery comes just two months after asbestos was discovered in an accessibility tunnel in the Joan Sutherland Theatre prompting a similar walk-off.

"Two months after this major safety issue was uncovered, and the builder was ordered to rectify it by the safety regulator, we have again seen workers exposed to these carcinogenic fibres," ETU secretary Dave McKinley said in a statement.

There were two unexpected finds of asbestos this week, a spokeswoman for builder Laing O'Rourke told AAP in a statement.

"All procedures as defined in our asbestos management plan have been followed in consultation with the hygienist and the licensed asbestos removal company," the spokeswoman said.

The theatre construction site is now being inspected and all suspect materials submitted for testing before work resumes, Laing O'Rourke said.

SafeWork NSW confirmed it had been notified of the discovery.

It said workers had been wearing protective clothing when the asbestos was uncovered and, as a result, were not exposed.

"A prohibition notice was not issued as work had already ceased," a Safework NSW spokesperson said in a statement.

"However, SafeWork NSW inspectors are monitoring the situation closely and will take any action necessary to ensure the health and safety of the workers involved in the construction work."

The Sydney Opera House launched an investigation after the discovery in August and the builder subsequently obtained a clearance certificate declaring the site safe.