New Zealanders who have recently visited four countries highlighted as security risks will now need a visa to enter the United States.
Tighter travel rules for New Zealand and the 37 other nations that are part of the US visa waiver programme have come into force.
Those who do not usually need a visa will need to apply for one if they have been to Iran, Iraq, Sudan or Syria in the last five years or if they are dual-citizens of those countries and a visa waiver country.
The new measures were included in a bill passed by the US Congress last month.
They were brought in after concerns were raised that terrorists could take advantage of the visa waiver programme to travel to the US.
An estimated 20 million people use the programme annually to enter the US without a visa for business or pleasure for up to 90 days.
The new rules do not apply to diplomats or members of the military, and US officials can offer waivers to some travellers who visited the four countries because they work for aid groups, as journalists or have other legitimate business travel.