Fine Gael MEP Brian Hayes said a referendum on the future of Irish water is "unwarranted and would be bizarre."
Mr Hayes was responding to calls for a referendum to block any possible future privatisation of water services in Ireland.
Article 10 of the Constitution deals with ownership of natural resources and referendum proponents such as the Greens are looking to amend this to specifically block water privatisation.
However Mr Hayes says there would be logistical issues with a referendum on water.
"The people who are looking for a referendum - I don't think they've really thought it through a to what's the proposition you'd put [in it].
"When would you have it? Would it be added to other referendums? What happens if it went down - does that mean the Irish people are in favour of privatisation? I think it's bizarre … I don't think they've thought it through."
He insisted that legislation was the correct way to enshrine any such provision, and to "make sure that all the parties, come the next manifesto [for election] have this as a key promise."