Transport chiefs have been warned Wiltshire Council will formally oppose plans that risk "shunting" polluting vehicles from Bath onto its roads.

A new proposal would see even the cleanest HGVs weighing more than 12 tonnes charged to enter Bath's clean air zone – despite operators already securing funding through the council to upgrade six vehicles to the Euro VI diesel standard to avoid the £100 daily fee.

Leader Richard Clewer said he was not consulted and officers had fallen short of exploring "many other options available" to deal with any air quality hot spots.

His counterpart on Bath and North East Somerset Council, Kevin Guy, said he had always remained open to working with neighbouring authorities and suggested a meeting.

A report on the proposal to next week's cabinet meeting warned neighbouring authorities could bring a costly legal challenge against a unilateral decision to ban HGVs from Cleveland Bridge, but there was also a credible risk of opposition to the idea of tweaking the clean air zone.

That challenge did not take long to materialise.

In an open letter, Councillor Clewer wrote: "I will not condone any proposal which simply shunts polluting vehicles away from Bath on to Wiltshire's roads and has an adverse effect on communities and residents in West Wiltshire.

"I can confirm that Wiltshire Council will formally oppose any proposal that (to summarise Defra's guidance) '…results in the displacement of the most polluting vehicles…to surrounding areas'.

"The National Highways M4 to Dorset Coast Strategic study is in my view the only way to properly deal with this issue. I am very happy to work collaboratively with you in support of that study to find positive solutions to improving the highways network throughout the region."

Wiltshire Council previously objected to an attempt in 2012 to introduce a permanent 18-tonne weight limit on Cleveland Bridge.

The authorities fell out again after it refused to host a diversion during the ongoing £3.8million project to repair Cleveland Bridge, instead forcing traffic to use a route through South Gloucestershire.

Councillor Clewer accepted an invitation to meet Councillor Guy in October that Bath MP Wera Hobhouse said was a chance to "draw a line under the bad blood" between the two authorities.

Responding to the Wiltshire Council leader's letter, Councillor Guy wrote: "We have always remained open to working with your council and all neighbouring authorities.

"The report which will be considered by my cabinet next week sets out the aspirations of my administration and the basis for future conversations. "After you accepted our invitation to the Guildhall in Bath this year to discuss transport, you said you would reciprocate, I have not yet received any return invitation from you or your chief executive. "I would welcome the opportunity to meet with you and your officers to discuss the position in more detail and I hope we can arrange to do so as soon as possible." The clean air zone currently charges high-emission vans, private hire vehicles and taxis £9 a day to enter, while drivers of non-compliant buses, coaches and HGVs have to pay £100. Private cars are not charged. Some 1,495 drivers were eligible for funding to replace or their vehicles retrofit, and around 600 have already been replaced – including six HGVs weighing 12 tonnes or more. BANES Council said it had expected to upgrade 108 HGVs in its medium uptake scenario, "but the sector has responded so well without this support". Cabinet members will consider the proposal to amend the clean air zone on December 15.