Roscommon Galway TD Michael Fitzmaurice believes the plans will mean that farmers can only produce 170kg of organic nitrogen per hectare of farmland.
EU plans to alter the nitrates directive in Ireland will be discussed when Minister Charlie McConologue appears before the Oireachtas Agriculture Committee today.
Ireland currently has a derogation agreement that means some farmers have been permitted to produce 250kg.
The EU Commission says the derogation would fall to 220kg from January 1st - leaving farmers with three options - reduce the herd, buy more land or find someone to take slurry from their farms.
Deputy Fitzmaurice says Irish farmers need certainty or else young people will leave the sector.