Government proposals to value TB reactors using a category card system based on average GB market prices, have been rejected as unfair by the industry.
Farmers claim the system will turn disease compensation into a lottery with some animals undervalued and others overvalued.
Pay-outs - for bovine TB, brucellosis, BSE and enzootic bovine leukosis - will depend on the animal's age, sex, pedigree status and sector.
Similar plans were put forward for consultation last year but there are now 29 valuation categories for cattle as opposed to the previous 10.
NFU Cymru insists the only fair way to assess animals is at slaughter by an approved valuer. Mansel Raymond, NFU Cymru milk board chairman, said: "Twenty-nine arbitrary categories covering the vast diversity of the Welsh dairy and beef industry is an insult."
National Beef Association chairman Robert Robinson described the system as "seriously flawed and inadequate".
He added: "It is obvious that Defra, in particular, is unhappy with individual valuation because it feels it has been cheated in the past."
NFU Cymru's milk board believe the proposals have been introduced to curb rising TB compensation bills. Nearly 4,000 cattle have already been slaughtered in Wales between January and September this year.
Mr Raymond said: "We as cattle farmers are being asked to pay the cost of the Welsh Assembly's refusal so far to take control of the escalating problem."
But Wales countryside minister Carwyn Jones insisted that, despite an annual bill of £10m, there were no plans to cut TB payments.
He pledged to implement main recommendations of the cross-party EPC committee report on TB in Welsh cattle. However, critics have claimed the
Assembly is promising more than it is delivering.
Next spring it will consult on premovement testing of cattle and examine how Intensive Treatment Areas can be established. Gamma Interferon testing, another key recommendation, is to be trialled.
NFU Cymru wants annual testing and is concerned that its Meirionnydd branches recently received a Defra brochure saying testing would be on a four-year cycle.
County chairman Huw Roberts said: "This will potentially create a continuous catch-up situation until the disease spirals totally out of control."
But Carwyn Jones insisted TB measure must be "practical, proportional and sustainable" - and must be part-funded by farmers.
