More than 500 Sydney council workers have walked off the job over concerns about the weed killer Roundup.

Outdoor staff at Blacktown City Council last month stopped using glyphosate-based sprays like Roundup after other local councils banned the product and begun trialling safer alternatives, according to the United Services Union.

The union representing council workers said the dispute “escalated” this week when management ordered six staff to either use the product or be moved 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.

“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.

“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 owns Roundup, says the weedkiller’s active ingredient glyphosate is safe for human use and not carcinogenic.

The company faces lawsuits by tens of thousands of plaintiffs around the world, and recent Roundup jury verdicts against Bayer have already caused its share price to plummet.

One of the Australian plaintiffs is 54-year-old Victorian gardener Michael Ogalirolo, who used the chemical regularly over the course of several decades, and has now developed non-Hodgkins lymphoma.