Travellers are warned to expect delays upon arrival at the country's largest airport as hundreds of security workers walk off the job.
Security workers at Sydney Airport's domestic and international terminals will undertake two four-hour stoppages on Friday.
The workers, contracted by the airport from security firm Certis Group, are demanding more full time jobs, fairer rostering and no cuts to hours.
"There will be delays," Transport Workers Union national secretary Michael Kaine told ABC from the airport on Friday morning.
"These workers regret that. They don't want to have to take this strike action but they are forced to."
The industrial action comes following months of enterprise agreement negotiations between Certis, its staff and the union.
The union claims job insecurity and limited pay have left some critical security staff fatigued and forced to work multiple jobs.
"This is not just about the security and safety of these workers," Mr Kaine said.
"It's about the security and safety of all passengers flying in our airways, and we've got to make sure that we get that recipe right."
Certis Group, meanwhile, claimed it remained committed to negotiating in good faith and had put a fresh offer to staff as recently as Thursday.
"We are disappointed that, with that offer on the table, the TWU has chosen instead to proceed with industrial action that affects the travelling public," a spokesperson told AAP.
But Mr Kaine said crisis talks on Thursday had failed to yield results, as the security company pressed ahead with plans to cut minimum hours by six hours per week.
"Aviation jobs used to be secure jobs for life," he said, while standing before a large crowd of Certis Group workers.
"Over the last 10 or 15 years, airports and airlines have decimated these standards."
The union has also demanded Sydney Airport, which is not party to the negotiations, step in to improve pay and conditions.
"The blame here lies squarely at the feet of Sydney Airport," Mr Kaine said.
"When you're making half a billion dollars worth of profit, but you're squeezing the contracting companies that are providing the services to the Australian public, you are the one to blame."
A spokesperson for Sydney Airport said it was working with its partners to minimise disruption and maintain passenger safety.
"We recommend passengers travelling today allow extra time and stay alert for messages from their airline," they told AAP.
The negotiations spilled over into a series of separate walk-offs from the airport in late September, involving a reported 400 staff.
Security staff, including those working in passenger and operational screening functions, are expected to strike from 6am to 10am and 5pm to 9pm.
