NBN technicians have walked off the job over work conditions including claims of pay cuts.
The Communications Electrical Plumbing Union said 200 of its members met in Sydney's west on Monday and voted to take immediate industrial action, with others dialling in from around the country.
CEPU national president Shane Murphy said the members cited ongoing issues with the NBN, pay cuts and a '"shambolic" dispatch system as the source of their frustrations.
Mr Murphy said NBN's contracting arrangements had left subcontractors out of pocket.
"It comes on top of $77 million worth of bonuses paid (to NBN executives) at the same time they've got their delivery partners cutting the pay rates of contractors, having a dispatch system that's delaying contractors from servicing their customers which affects the amount of jobs they're doing and their take home pay," Mr Murphy told AAP.
He expects about 500 technicians who sub-contract to the NBN to take part in the action across the country.
"The numbers are continually growing by the minute, as (sub-contractors) become more aware of the action taken by the majority of their mates," he said.
"These small business owners simply can't afford to go to work. It's an appalling situation in particular on a government project and there needs to be an inquiry by the parliament."
Technicians cancelled appointments across the country on Monday and its unclear when they will return, he says.
Dozens of technicians, some carrying CEPU flags, turned up to NBN Co's North Sydney headquarters demanding a meeting with management.
The NBN said it had thousands of technicians working for the company across the country and many were continuing to work on Monday.
"NBN Co appreciates the ongoing dedication and diligence of the thousands of highly qualified field technicians and network engineers who work hard to maintain the reliability and performance of the NBN network across Australia," the company said in a statement.
"NBN Co would like to assure customers that it does not expect this morning's meeting convened by the CEPU to have any impact on normal NBN network operations, new connection or assurance orders to rapidly correct any network faults that may arise.
"We are working constructively with the CEPU and we are seeking to maintain and support strong, productive working relationships with our delivery partners and their respective subcontractors."