The Maori Party says Labour has to sort out who owns freshwater before its begins taxing it.
"You can't start charging for something you don't own," co-leaders Te Ururoa Flavell and Marama Fox said in a statement tonight.
Labour had said it would respect iwi rights in relation to water.
"If that is the case, then those rights and interests need to be determined before anyone starts taxing water.
"Any discussion around water rights, interests, management, quota, ownership, pricing or quality must involve hapu and iwi and the same goes with any potential land tax."