Concerns have been raised that a clean air zone (CAZ) could increase traffic in nearby towns.
Wiltshire Council fears drivers will avoid paying to enter the centre of Bath by using smaller roads.
Council lead Phillip Whitehead said the CAZ, which starts on 15 March, "must not" impact air quality in Wiltshire.
Bath and North East Somerset Council (BANES) said it had asked the government to help pay for air quality tests.
Bradford-on-Avon and Westbury are the areas Wiltshire Council says it is most concerned about.
Mr Whitehead said: "We need to have this monitoring in place now, and if this monitoring shows that there is an adverse impact on Wiltshire's roads, we also need Bath and North East Somerset Council's assistance in addressing this."
From 15 March, commercial vehicles that do not meet the required emissions standards will pay a daily charge to drive in the centre of Bath.
High-emission commercial vans will pay a £9 fee and HGVs and buses £100 in what will be England's first charging CAZ outside London.
Private hire vehicles and taxis will also have to pay £9 per day.
'Request was rejected'
Mr Whitehead questioned the results of a Banes survey that showed the impact of the zone on surrounding communities would be 'neutral'.
He said: "We asked BANES to extend its monitoring of the area to allow us to gain a better understanding of wider HGV diversions, due to the significant costs associated with this monitoring, but this request was rejected.
"We have since reiterated this call."
In a statement, BANES said: "The technical modelling for the CAZ was submitted and verified by both government and the Technical Independent Review Panel to ensure that the conclusions were robust.
"We requested funding from government for monitoring of air quality in West Wiltshire. This request was turned down.
"We continue to liaise with DEFRA and have written to the Minister, lobbying on behalf of our neighbour."
The council emphasised it was introducing the clean air zone because of a government directive to improve the city's air quality.