Sydney workers have faced a chaotic commute as about 1,200 public bus drivers go on strike for 24 hours.

Despite a late-night ruling by the New South Wales Industrial Relations Commission that their action was illegal, the drivers walked off the job at midnight.

They are protesting against the Berejiklian Government's planned privatisation of services, primarily in Sydney's inner west.

Routes affected: 401, 406, 407, 408, 412, 413, 415, 418, 422, 423, 425, 426, 428, 430, 431, 433, 436, 437, 438, 439

401, 406, 407, 408, 412, 413, 415, 418, 422, 423, 425, 426, 428, 430, 431, 433, 436, 437, 438, 439 441, 442, 444, 445, 460, 461, 462, 463, 464, 466, 470, 473, 476, 477, 478, 479, 480, 483, 487, 490

441, 442, 444, 445, 460, 461, 462, 463, 464, 466, 470, 473, 476, 477, 478, 479, 480, 483, 487, 490 491, 492, 493, 495, 502, 504, 508, 526, L23, L28, L37, L38, L39, M20, M30, M41, X04, X25

491, 492, 493, 495, 502, 504, 508, 526, L23, L28, L37, L38, L39, M20, M30, M41, X04, X25 All school services in the inner west and Sydney south

All school services in the inner west and Sydney south If travelling to Sydney Airport, the 400 (Bondi Junction to Burwood) is impacted. Please catch the train. Modified services: The following services will be available along Parramatta Road in the peak period between 6.00am and 10.00am and 3.00pm and 7.00pm

The following services will be available along Parramatta Road in the peak period between 6.00am and 10.00am and 3.00pm and 7.00pm 438 - Five Dock to Railway Square

438 - Five Dock to Railway Square 461 - Burwood Depot to Railway Square

Industrial action stopped all bus routes and school runs in the inner west, and also bus routes in the south of Sydney, with commuter chaos set to continue in the afternoon.

Transport Minister Andrew Constance said he was unhappy about the move.

"The message I would say very clearly to drivers today is 'no work, no pay' and you'll stand condemned if you leave schoolchildren on bus stops and commuters are left hanging," he said.

Commuter Kate Duthie said she had not heard or seen anything warning of the strike.

"I'm a bit frustrated because I'm going to be late for work. I understand it's all about privatisation, and I don't really agree with that in terms of public transport because it forces prices up and it turns into a competition," she said.

"I'd rather they stay public. They do a good job and we rely on them."

Commuters are being told to catch the train or make alternative arrangements for the evening commute home.

'This matter is on his head'

Sydney already has a notorious reputation for its gridlocked streets and the Transport Management Centre warned traffic would get heavier today as parents drove their children to and from school.

Transport Management Centre spokesman David Wright said changes had been made to help school children.

"We've opened up the school Opal pass, which is usually only able to be used on buses, it can be used on an alternate mode of public transport," Mr Wright said.

"We've got extra light rail services running, we've even got a stand-by train coming from the eastern suburbs in the event it gets really busy."

The Rail, Bus and Tram Union has apologised to commuters for the strike.

It said members were angry that neither they nor commuters were consulted before inner-west bus services were flagged for privatisation earlier this week.

There was not much action at Leichhardt Bus Depot in Sydney's inner-west this morning. ( ABC News: Mark Reddie )

Chris Prestons from the bus union said the Transport Minister was to blame for the disruption.

"This matter is on his head and we apologise for the disruptions this will cause the inner-west community and we ask for them to show patience for the drivers and to also put their anger towards Minister Constance," he said.