A call to increase the road tax on four-wheel drive vehicles has been criticised as damaging to rural Wales.
MP Norman Baker's campaign is aimed at 4x4s used in towns
Liberal Democrat environment spokesman Norman Baker urged a raft of new laws to control the sale and use of 4x4s.
Conservative Mid and West Wales AM Glyn Davies and the Farmers' Union of Wales said farmers in rural areas would be hardest hit by any changes.
"Yet again the Liberal Democrats at Westminster are campaigning against the interests of the rural community," said Mr Davies.
"Mr Baker has launched a campaign against four-wheel drive vehicles which in areas such as Montgomeryshire are essential because almost every farmer must own one to haul livestock.
"This is a straightforward anti-countryside policy which would hit livestock farming areas in particular.
"I don't expect the Labour Government to take the slightest notice of such obvious nonsense but it is deeply irksome to hear a political party which represents a large chunk of rural Wales advocating policies so obviously damaging to its economic well-being."
A report by Mr Baker, MP for Lewes in Sussex, called for higher brackets of vehicle excise duty for vehicles that produce high levels of carbon dioxide emissions.
Conservative Glyn Davies says changes would hit farmers hard
"4x4s leave a bigger footprint on the environment that other vehicles and can intimidate pedestrians, cyclists and other road users," he said.
"They are taking up space in town centres where there is precious little room for these children, our environment and historic towns."
All vehicles registered after 1 March 2001 are now put into six tax bands depending on the amount of carbon dioxide they emit, ranging from £65 to £165.
Mr Baker wants more bands to be introduced so that people owning 4x4s with higher emissions pay more tax.
Accepting that that rural communities would be afected by the tax, Mr Baker added: "Increasing the tax bands would make people consider which vehicle they should buy to help protect the environment."
An FUW spokesman said its members would be deeply concerned by any attempt to impose another tax on their way of life.
4x4 CO2 emissions g/Km
Volvo XC 90 - 242
Toyota Land Cruiser - 277
BMW X5 - 259
Mitsubishi Sogun - 251
"Four-wheel drive vehicles are essential workhorses for all farmers, they simply can't do their job without them," he added.
"A problem seems to have arisen because these vehicles are becoming increasingly popular with families in our large towns and cities.
"In some cases they appear to be little more than fashion accessories, and certainly never get a trace of mud on their wheel arches.
"The demand to increase the level of taxation on these vehicles appears to be designed to drive these vehicles out of the city limits.
"But the truth is that it's an ill-thought out campaign that will hit farmers and others who live and work in the countryside hardest of all."