ALBANY — New York voters gave a resounding thumbs down to a constitutional convention on Tuesday, once again rejecting an opportunity to open the state’s founding document to a full-scale overhaul after opponents stoked fears that such a convention could result in lost rights and benefits.

With most of the state’s election precincts reporting, “No” voters had easily defeated the ballot measure — known as Proposal One — with more than 80 percent of the vote.

The campaign against the constitutional convention drew a diverse collection of opponents, including conservative political groups, major labor groups like the A.F.L.-C.I.O., and liberal stalwarts like the New York branch of Planned Parenthood and the New York Civil Liberties Union. And while their concerns were often different, the basic logic of the anticonvention forces was similar: Such a convention could result in an erosion of protections for everything from collective bargaining rights to free public education.

A spree of advertisements called the convention a “con’s con,” suggesting that it would be vulnerable to back-room and unsavory deals. Opponents argued that the convention could cost hundreds of millions of dollars, which seemed to be an exaggeration, but the message proliferated on “No on Prop 1” lawn signs throughout the state.