Labour Leader David Shearer said he saw the tattoo in a television report: "I couldn't see anything wrong with it."
Mr Shearer said a lot of people had tattoos now, including singer Gin Wigmore who had been used in Air NZ advertising.
"I actually thought the tattoo was rather lovely."
Maori MPs also criticised the airline's policy.
National MP Tau Henare said that Air NZ was "cutting off its nose to spite its face".
"It's a beautiful piece of art that she has on her forearm and I don't think that any tourist would go scurrying for shelter if they saw her moko."
Labour MP Shane Jones said that tattoos were the "new norm" for young people, noting that his daughter had a tattooed chin.
"With the changing demography, I think businesses are going to change as well because there's more and more young women who sport moko that are going to have to be employed somewhere."
He added: "I don't think the moko should be seen as a sign of dishonesty or danger or potential anarchy in the air. it's just part of identity."
Ms Nathan said she never thought her ta moko - depicting her heritage and her two children - would limit her career choices.
"I thought that they would be quite proud to have someone with a ta moko working and representing New Zealand. [But it's] not the case. [It] was the total opposite."
Ms Nathan said she was told tattoos that could not be covered by the Air NZ uniform were unacceptable.
"I said straight away, 'This is a ta moko.' She [the interviewer] said, 'You can't even cover that up' and that 'we will have to stop this interview.'
"I was totally shocked and just couldn't believe what I was hearing."
Air New Zealand said tattoos were seen as "frightening or intimidating" in many cultures.
"Naturally we want all of our customers to feel comfortable and happy ... and this has been a key driver of our grooming standard which, like many other international airlines, prevents customer-facing staff from having visible tattoos."