More than 500 workers at a Sydney council have walked off the job after management allegedly refused to heed their concerns over the use of glyphosate-based weed killer Roundup, which has been linked to cancer.

Outdoor staff at Blacktown City Council last month refused to continue using glyphosate sprays, urging management to follow the lead of other local councils which have banned the product and begun trialling safer alternatives, the United Services Union said in a statement.

The union, which represents council workers, said the dispute "escalated" on Wednesday after management ordered six staff to either use the product or face being forced into alternate jobs.

"Outdoor staff responded by halting work and returning to their depots, leaving more than 10,000 bins uncollected," a statement from the union said.

Staff are expected to meet on Thursday to decide whether they will continue their protest.

"Around the world, governments, companies, and individuals are abandoning the use of glyphosate because of the growing evidence that it is responsible for causing cancer," union secretary Graeme Kelly said.

"Yet management at Blacktown City Council have refused to listen to these concerns, instead attempting to stand over workers to force them to use a potentially dangerous product."

Bayer, which bought Roundup maker Monsanto for $63 billion last year, says Roundup's active ingredient glyphosate is safe for human use and not carcinogenic.

The company faces lawsuits by more than 13,400 plaintiffs in the US and globally and a series of Roundup jury verdicts against Bayer have prompted its share price to plummet.

Among the Australian plaintiffs is Victorian gardener Michael Ogalirolo, 54, who regularly used the herbicide between 1997 and 2018 and who has developed non-Hodgkins lymphoma.

Mr Ogalirolo filed a writ in the Victorian Supreme Court in June alleging Monsanto Australia Pty Ltd failed to warn its Roundup Products are dangerous to human health, including that it could cause cancer.