Blacktown City staff refused to continue using glyphosate weedkillers due to cancer concerns.

A Sydney council says it will trial a new weedkiller after more than 500 workers walked off the job due to concerns over the use of the glyphosate-based Roundup.

The union which represents council workers said outdoor staff at Blacktown City Council last month refused to continue using glyphosate weedkillers, including Roundup, due to safety concerns.

The United Services Union said the “dispute escalated” on Wednesday after management ordered six staff either to use the product or be forced into alternative jobs, resulting in a number of employees stopping work.

The council sought an urgent hearing in the Industrial Relations Commission on Thursday morning after garbage bins were not collected and some outdoor services were disrupted due to the industrial action.

On Thursday afternoon the council announced the commission had endorsed an agreement with the union under which the workers would return to their jobs as long as the council implemented a trial of a “viable alternate weed control product”.

One of the council’s crews will use the alternative product while others continue to use a glyphosate-based product, the council said in a statement.

“Council is continually monitoring the situation and will act according to the recommendations of the regulator and on the findings that result from the trial,” Blacktown’s mayor, Stephen Bali, said in a statement.

“We have agreed to trial viable alternatives. What is important for everyone to understand is that council will not place employees or members of the public at risk.”

Bayer, which bought Roundup maker Monsanto for $US63bn in 2018, has said Roundup’s active ingredient, glyphosate, is safe for human use and not carcinogenic.

But 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 caused its share price to plummet.

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

Ogalirolo filed a writ in the Victorian supreme court in June alleging Monsanto Australia failed to warn its Roundup products were dangerous to human health.