The Â£2.3m programme spearheaded by Mayor George Ferguson is nearly half complete, with 20mph zones operating in areas such as Clifton and Redland.
But Tory councillor Lesley Alexander wants the rollout stopped for a scientific assessment of their effect and impact on road safety.
Mayor Ferguson said the scheme's efficiency was already under review.
He said regular traffic counts, speed counts and household interviews were being undertaken, and local support for the zones was "clear".
Ms Alexander said the road safety case for the zones was not "conclusively confirmed" by either of the two pilot trials conducted in Bedminster and east Bristol.
She said with recent reports suggesting these speed limits were "actually making roads more dangerous", she was calling on the mayor to "urgently stop and assess the efficacy of the controversial speed zones".
She said a "more targeted approach" should be taken, with speed limits "only installed in places of obvious sensitivity or where there is local demand".
Campaign group Alliance of British Drivers has called for the government to halt the rollout of 20mph zones following increases in 20mph accidents.
However, Mayor Ferguson said the reduced speed limits introduced in Bristol were "undeniably helping to make streets safer and improve quality of life for local communities".
Areas including Eastville, Frome Vale, Hillfields, St George and Fishponds are expected to adopt the zones before the end of the year.
In January, many roads in the centre of Bristol and in Clifton, Cotham, Bishopston and Redland had the speed limit reduced from 30mph to 20mph.
The city-wide roll-out is due to be completed by March next year.
The rollout of 20mph traffic zones across Bristol should be halted, according to Conservative councillors.