Green Party Councillor Gus Hoyt questioned Mayor George Ferguson on the use of glyphosate by the council and its contractors in September. The council is yet to disclose full details of what is applied where, and at what cost, the alliance said in a press release.
A Freedom of Information request filed by Playsafe Bristol has also not been answered within the statutory 20-day time limit, the statement said. A council spokesperson confirmed this and said an investigation was being carried out into why the deadline was not met.
Harriet Williams of PlaySafe said the city's residents have a right to know what chemicals are being sprayed in their city.
"It seems inconceivable that the council either does not know or will not disclose data on what chemicals are applied to our public spaces – particularly as its own pest management policy says full information will be made available to the public."
Williams added: "It is entirely possible to wean ourselves off chemical weed control in public spaces. Cities like Paris, Chicago and Vancouver are already doing it, and as European Green Capital 2015 it would be brilliant if Bristol followed suit."
The group is surveying public opinion regarding urban pesticide use.