National Party leader Simon Bridges said the decision to hold the referendum at the same time as the election was a "cynical" move, and he wouldn't be surprised if it was designed to distract voters from key issues.
"Pretty cynical that you've got a Government that wants to distract from the core issues of a general election like who's best to govern ... and core issues around the economy, tax, cost of living, health, education and law and order."
He said the Government was already decriminalising drug use by promoting police discretion in prosecuting people who are caught with drugs, which was announced last week.
"Right now, if someone is smoking cannabis outside a school, what are the consequences? What's the message from this Government?" Bridges said.
The Government is also looking at holding referendums on electoral reform and euthanasia, though no decisions on those issues have been made.
Asked if the Government was trying to deliberately overshadow the election with referendums, Bridges said it wouldn't surprise him.
"They know their record on big stuff doesn't matter ... We may well have three [referendums], as they seek to distract from choosing a Government that's best going to lead on the big matters."
Bridges said he would vote against the use of recreational cannabis - though he had never used it - because of the "normalisation" message it sent and the impact it might have on mental health.
Little has previously said that a citizens' assembly process - nationwide meetings used in Ireland on the issue of abortion - to stir public debate was an option, but the Cabinet had decided against it.
"So we won't be using that mechanism in terms of public engagement, we will have other ways of getting the public debate going," Little said.
He added that it is not an area that needed a lot of policy development as it has all been done.
Asked about a binding referendum on euthanasia, Little said that was a matter for Act Leader David Seymour and the select committee that is considering the euthanasia bill.
Seymour has a member's bill on euthanasia currently going through the house.
"David has told me that he fully expects that there will be a referendum clause in that bill when it gets reported back."
Little said the coalition partners were still to decide on a referendum on electoral reform.
He said the electoral commission has put together a Budget bid for the cannabis referendum for next year, which would be processed with other Budget bids.
But he said because of budget confidentiality, nothing can be detailed on its Budget until May, when the 2019 Budget is released.
