"The air is just too poor," Mr Keating said. "And it's not just me saying it, it's the health department." Loading Mr Keating said at least one of the operators had warned it could take action against the union: "To say this is some sort of illegal action is just disgraceful." Mark Hulme, General Manager Operations at DP World Sydney - one of the three terminal operators at Port Botany said road and rail operations were not affected by the union action. "Employees engaged in waterside operations ceased work at approximately 1.30pm and have yet to resume," he said. "This action is occurring port-wide."

"Discussions with the employee representatives are continuing in accordance with our dispute resolution procedure," Mr Hulme said, adding the company was hopeful work would resume "with minimal further disruption". "It remains our view that the actions taken by employees to cease work is inconsistent with the provisions of our enterprise agreement that deal with resolution of disputes. "Those employees participating in the stoppage have been stood down off pay." Allen Hicks, national secretary of the ETU, said many parts of Australia were currently affected by smoke from bushfires. “We have informed out members that they should protect their health and stop work if they are concerned about exposure to bushfire smoke in their workplace," he said.

Loading Sydney had been ranked as among the worst ten cities in the world for air quality at times over the past few weeks, Mr Hicks said, with effects such as irritation to the eyes and throat for those outside. “Bushfire smoke also contains particles which can affect lung health, particularly for people who already suffer from conditions such as asthma or emphysema," “Furthermore, these particles can place extra stress on the heart - leading to increased risk of heart attack," he said. Construction Forestry Maritime Mining and Energy Union (CFMMEU) NSW secretary Darren Greenfield said the union had sent out alerts to members and has not previously had to deal with smoke conditions, until recent weeks.

"It was a new experience for us," he said. "We have taken a stand with inclement weather in the past.

"We have advised members that anyone planning to do overtime to knock it on the head today." CFMMEU members have been advised to download air quality aps onto their phones. A spokesman for Health NSW said it was "a duty of care for employers to make sure employees have a safe workplace". "Our advice is don't be in it is the best way to avoid health issues," he said. The standard health advice remains particularly for those with respiratory issues to avoid strenuous activity outside and to have their medicine handy, the spokesman said.