The Green Party is expecting the new National-led Government to push through radical changes to weaken environment and workplace protection laws.
National has a one-seat majority in the House before special votes are counted, with 61 seats in a 121-seat Parliament, and will be able to pass whatever legislation it wants.
Even if that were to change after special votes are counted, Prime Minister John Key is gathering support from previous partners.
Although Mr Key says his new administration would not be veering off to the right, Greens co-leader Russel Norman said National would further undermine environment and employment protection.
"I've no doubt that the National Party will go further than previously intended or signal, rather, in terms of weakening environmental protections, in terms of weakening protection around workers' rights - they'll use their single vote majority to push through some quite radical changes."