NFU CYMRU is calling for concerted action to curb illegal, damaging and dangerous use of common land by drivers of off road vehicles and motorbikes.
Because cross compliance regulations apply to commons, the union fears that the single farm payments of farmers with grazing rights will be compromised.
In Wales 180,000ha, or 10.7% of the land area, is registered common, and a significant part of is located close to the heavily populated M4 corridor in south Wales.
Graziers have complained for many years about a host of problems, including keeping stock on commons following damage to boundary fences and dry stone walls, illegal shooting and widespread fly tipping.
More recently they have reported a sharp increase in the number of stock killed by motorists speeding on roads crossing common land, and about growing use by motorbikes and 4x4s.
“Significant amounts of top soil have been lost due to off road use by motorbike riders, leaving the surface of commons liable to further erosion and water logging,” said William Jenkins of Monmouthshire NFU.
He took local Welsh Assembly member Irene James on a fact- finding visit to Manmoel Common near Blackwood as part of the union‘s campaign for joint action against, what the union described, as an escalating menace.
He and other members expressed concern for the safety of people using the common legally, and about the number of livestock being injured and killed.
“I envisage a scenario where farmers like myself will no longer wish to graze their livestock on the common due to the reckless behaviour of a small number of people, and this could have a significant impact on our incomes and the environment of the common,” Mr Jenkins said.
What was needed was joint action by graziers, local authorities, police forces and the Welsh Assembly.
It was the only way curbing the illegal, dangerous and anti-social activities of a minority on urban fringe commons.