Wellington's Te Papa says it is advising pregnant or menstruating women against attending one of its tours "for their own safety."
An invitation for regional museum staff to go on a behind-the-scenes tour of some of Te Papa's collections included the condition that "wahine who are either hapu [pregnant] or mate wahine [menstruating]" were unable to attend.
Te Papa spokeswoman Jane Keig said the policy was in place because of Maori beliefs surrounding the taonga Maori collection included in the tour.
"There are items within that collection that have been used in sacred rituals. That rule is in place with consideration for both the safety of the taonga and the women," Keig said.
She said there was a belief that each taonga had its own wairua, or spirit, inside it.
"Pregnant women are sacred and the policy is in place to protect women from these objects."
Women who plan to attend the tour on November 5 are expected to be honest about whether they are pregnant or menstruating as a sign of respect to Maori beliefs.
Te Papa insists the request is not an outright ban.
"If there are pregnant women who want to go on the tour we don't stop them. But we do prefer they respect the belief." Keig said.
The policy is not in place for the general exhibition.
The email sent to regional museums offered women who were pregnant or menstruating the chance to go on the tour at another time.
Feminist blogger Bogannette said she was disgusted by the museum's stance.
"It's disgusting that in this day and age women can be told they're "forbidden" for menstruating or being pregnant. It's a completely archaic belief that is oppressive to all women."
She said she would encourage women who are pregnant and menstruating to attend the event.
"Are they going to check to see if a woman is menstruating? A belief that there is something wrong with women if they are menstruating or pregnant is ridiculous. "
"Te Papa is taxpayer funded. It's a public museum that is supposed to be inclusive of everyone. Religious and cultural beliefs should be ignored if they're going to insult or oppress women for any reason."
However, Margaret Mutu, head of Maori Studies at Auckland University, said women should not be offended by the request.
"The reproduction area is extremely powerful and can do damage to things that are not tapu. It's about the power of women, not about stopping them."
Mutu said the objects were obviously dangerous and the hapu they came from would have told the museum about how to treat them.
Mutu said in her hapu, women were also prevented from going onto gardens or fishing areas while tapu.