Australians have been unlawfully charged for managed isolation stays in New Zealand because of an error in what the National Party is calling a shoddy law.

The government has passed legislation under urgency today to fix the problem, which it estimates affects up to 650 people.

The law was initially brought in in August to allow people to be charged for MIQ in certain circumstances, such as New Zealanders going overseas for short trips.

Australians coming into the country as critical workers were also charged but the law did not properly allow for that.

National Party Covid-19 response spokesperson Chris Bishop says it was frustrating to be sitting in parliament unnecessarily, debating the law retrospectively, when it should have been done properly in the first place.

"This is a shoddy bill, shoddily put together by this shoddy government," he says.

Covid-19 Response Minister Chris Hipkins says it was regrettable to have to make the change, but it was purely technical and did not mark any change in government policy.

The intention was always that the Australians should have been charged and it was important to ensure their fees were valid, he says.

- RNZ/Rowan Quinn