The Law Society has lambasted a provision in three waters legislation making it more difficult to privatise water assets.
It would take agreement from 60 percent of MPs to change, when a simple majority is needed for all other legislation - bar some electoral law matters.
RNZ has approached Local Government Minister Nanaia Mahuta for comment.
The clause was introduced by the Green Party, who are defending it, but it has prompted outrage from the opposition and legal scholars.
Law Society president Frazer Barton has written to Mahuta calling the move "constitutionally objectionable" and in breach of well-established Parliamentary norms.
Entrenchment hindered future government's policy decisions and "undermines democracy", Barton said.
He was also concerned about the use of urgency to speed up the passage of the bill through Parliament, which he said left no room for cross-party dialogue or public consultation.
Barton strongly urged the government to recommit the Bill to the Committee of the Whole House before its third reading, and to remove the entrenchment provision.
Green MP Eugenie Sage, who proposed the entrenchment clause, agreed entrenchment should be reserved only for matters of utmost importance.
"Retaining the public ownership of water assets is of prime importance to New Zealanders, and the Greens believe meets this threshold."
Mahuta told the House that while it "may not pass the constitutional threshold, there is a moral obligation of people who believe that privatisation should not occur to support that particular [clause]".
Prime Minister Jacinda Ardern said Parliament's Business Committee would take it up and "resolve the issue".
But political commentator Peter Wilson writes the committee cannot fix it.