Two Sydney councils in traditional Liberal heartland will use council elections to conduct a referendum on council mergers, adding to mounting pressure on the Berejiklian government over the controversial policy.

Alongside electing councillors, ratepayers in Hunters Hill and Lane Cove will be asked if they support the state government's proposed merger in a separate poll at the September council elections.

Local Government Minister Gabrielle Upton says the government remains committed to the remaining mergers, which have been delayed due to legal action.

It comes as some Sydney mayors foreshadow scaled-back elections and difficulty in attracting quality candidates due to the ongoing uncertainty over the future of their councils.

The referendums will be the first time entire communities have been polled on their views on council mergers, more than a year after the then-Baird government rolled out the policy in May 2016.