NFU Cymru is to launch a legal challenge against Welsh government's new rules to control farm pollution having previously raised concerns about the lawfulness of the decision.
A nitrate vulnerable zone (NVZ) designation will be rolled out gradually across the whole of Wales, starting from 1 April.
NVZs are areas within Wales that contain surface water or groundwater susceptible to nitrate pollution from agricultural activities.
Agricultural pollution incidents 'remain very high', according to the Welsh government, averaging over three per week in the last three years.
It said some of these had led to the contamination of drinking water sources and the destruction of plant and aquatic life in parts of waterways.
But NFU Cymru has slammed the 'heavy and disproportionate' rules which would in turn 'punish' the whole farming industry.
President John Davies said: "We have put forward to Welsh government farmer-led voluntary initiatives, which have worked in the past, supplemented by targeted and proportionate regulation.
"Yet Welsh government has failed to take into account any relevant information and feedback from stakeholders.
“As a union we accept a regulatory backstop may be needed, but this must take in to account the regulation that is already operational.
"It must be evidence based, proportionate to the risk, and targeted to areas where water quality improvements are needed."
NFU Cymru said it was also disappointed at the lack of support offered to farmers in order to be able to comply with the new regulations.
It added that Welsh farmers faced having to find up-front costs of £360m and ongoing yearly costs of £14m a year, putting many family farms 'out of business'.
Mr Davies added: "The package of support to farmers to help make these drastic changes is woefully inadequate.
“It will affect every sector; every area of Wales and every farmer will be subject to draconian record keeping and complex restrictions on the day-to-day running of their businesses.
“This is why, along with our lawyers, legal panel firm JCP Solicitors and with support from our Legal Assistance Scheme, we have decided to ask the Courts of Law to look at these regulations.”