Prime Minister John Key says he expects the Government's tax cut package will roll out as planned, but is refusing to give firm assurances.
It is the first time doubt has been cast over the National Party's key election campaign policy.
This comes after questions about the Government's commitment to the annual $2 billion into the Superannuation Fund, given the worsening state of the Government's books.
On Thursday, Mr Key was asked to confirm if there will be tax cuts for the next three years.
He said the Government's current plan is the best way to stimulate economic growth and confirmed tax changes due on 1 April will go ahead.
However, he would not give a full commitment to tax cuts planned for 2010 and 2011.
Mr Key, who will attend the jobs summit in Auckland on Friday, says people are living in "dynamic" times and he does not want to engage in hypothetical debate about the future.
The Labour Party has seized upon the issue, saying if Mr Key had any courage, he would cancel all impending tax cuts and make sure the money goes to those who need it most.
Labour leader Phil Goff says the tax cuts are inequitable, as they favour higher income earners and the package should be scrapped.
Green Party co-leader Russel Norman says the Government's economic approach has so far been flexible and he would not be surprised if is taking another look at tax cuts.
National's support partner, the Maori Party, would be happy see a review of the programme. Party president Whatarangi Winiata says it could mean more money was put in the pockets of lower income earners.
National's other support partners, United Future and ACT, say there is no reason why tax cuts shouldn't go ahead.