Caltex Australia says it will close its Kurnell refinery in Sydney in the second half of 2014 as part of a supply chain restructure.
The company says around 330 jobs will be shed at its Kurnell operation over the next two years following a review announced in August last year.
As many as 300 contract positions will also be cut.
Kurnell is one of two large Caltex refineries, with the other located in Brisbane.
Caltex provides about a third of Australia's petrol.
The firm has been under pressure because of the strong Australian dollar and ageing industrial facilities.
National secretary of the Australian Workers Union Paul Howes described Caltex's decision as an attack on motorists.
"Caltex's announcement of (the) closure of Kurnell is a kick in the guts to every motorist we will respond at noon at the refinery," he Tweeted.