One of the state government's strongest supporters of council mergers is preparing to apply for a partial reversal of its own amalgamation.

Hornsby Shire Council was on Wednesday night due to endorse a proposal to formally request the government return a portion of council territory handed to the new City of Parramatta Council last year.

The Greens are calling for NSW Premier Gladys Berejiklian and Local Government Minister Gabrielle Upton to bring an end to council amalgamations. Credit:Louise Kennerley

The move is a reflection of the frustration felt by Hornsby Council, which has been an enthusiastic supporter of council amalgamations, about the government's failure to implement its policy. In particular, the government was defeated in the Court of Appeal by Ku-Ring-Gai Council, which was to have been merged with Hornsby.

The mayor of Hornsby, Steve Russell, said the result of the "whole sorry saga" of council mergers had been that Hornsby had reduced in size, and in financial capacity.