The Government remains committed to getting its books back into surplus in 2014-15, but opposition parties think it's already starting to waver on its target.
The Treasury is to issue the December half-yearly economic and fiscal update on Tuesday.
Radio New Zealand's political editor said the deficit in the first four months of this year was $169 million worse than predicted in the Budget.
Prime Minister John Key said the announcement will soon be out of date. Earlier in the month, he hinted the surplus target might be getting more difficult.
Green Party co-leader Russel Norman said National is now trying to wiggle out of its promise.
Labour finance spokesperson David Parker said that if the Government does not get back into surplus in 2014-15 it will have failed.