The Race Relations Commissioner says people must not assume someone's race by lumping them into one ethnicity group.
It follows National MP Amy Adams' apology to Catherine Chu, the party's Banks Peninsula candidate, for wrongly describing her as Chinese.
Chu was born in Christchurch and her parents are Korean.
Adams made the comments during an interview with MediaWorks about who would represent the Chinese community once Jian Yang retires.
Race Relations Commissioner Meng Foon told Morning Report that Adams should have checked the facts first.
"People do make mistakes but I know that when people think I'm Japanese I'm hurt because they didn't bother to ask."
A quick Google search would draw up some information on the candidate, he said.
"In a team like politics, they should know each other very well. Unfortunately, there's been a litany of mistakes."
He said people needed to do their research and ask people about their heritage, which was a way to find out about someone's cultural upbringing.
"It is a casual attitude of many people stereotyping, thinking that people ... are all one race or another."
He wouldn't call it racism, instead calling it was a mistake and stereotyping.
"Racism is learnt," he said.
"People need to admit that they have made a mistake. Before they open their mouths next time they need to actually do a bit of research."
In May, National Party deputy leader Nikki Kaye said Paul Goldsmith "obviously is of Ngāti Porou" when asked how many Māori MPs were in the shadow Cabinet.
But that was news to Goldsmith.
"My great-great-grandfather had European wives and Māori wives, and so I've got lots of relatives across Ngāti Porou - I don't claim to be Māori myself," he had said.