A Gisborne school's ban on dreadlocks and braids has been labelled "straight racist" by a local woman, who plans to lodge a complaint with the Human Rights Commission.

The ban was announced by Gisborne Boys' High School principal Tom Cairns this week, as part of a "blitz" on uniform and hair standards.

Cairns said "extravagant and unusual haircuts", including dreadlocks and braids, were not permitted as per the school rules.

"Students with long hair must have it tied back. Hair should be the student's natural colour, not dyed or streaked," he posted on the school's Facebook page.

The requirements were outlined to the students at an assembly last term and again on the first day back.

The Herald has contacted the school for comment.

Taking the matter to Twitter, Tairāwhiti resident Tina Ngata, an indigenous and human rights advocate, called the school's words and actions "straight racist".

Ngata said she would be writing about it to the Human Rights and Race Relations Commission.

The Ministry of Education Te Tai Whenua (Central) hautū (leader) Jocelyn Mikaere said the school's board of trustees must not discriminate against students' culture or religion.

"Boards of Trustees have the authority to make and apply school rules on a wide range of matters including uniforms and appearance. This can range from hairstyles, clothing and tattoos," she said.

Mikaere said the ministry did not require schools to inform it about their rules, however, "we do expect them to communicate the school rules clearly to parents and caregivers and require schools to consult if they are proposing any changes".

A spokesperson from Human Rights Commission said while school boards had the discretion to set policies as they see fit, these policies must be consistent with New Zealand human rights law and consistent with Te Tiriti o Waitangi.

"The Human Rights Act (HRA) prohibits discrimination in education where a student is treated less favourably because of one or more of the 13 prohibited grounds under the Human Rights Act," the spokesperson told the Herald.

"Hairstyle on its own is not a prohibited ground. However, if schools restrict students from wearing their hair in a way that connects to their cultural, ethnic or religious identity, then it could be grounds for discrimination under the Act."

Lucan Battison (right) was all smiles with his lawyer Jol Bates (left) after defeating St John's College in court in 2014. Photo / Mark Mitchell

The High Court has found that schools need to carefully consider whether any rule regarding hair or appearance would breach a student's right to freedom of expression under the New Zealand Bill of Rights Act 1990 or breach their right to dignity and individual autonomy, the spokesperson said.

Then Year 12 student Lucan Battison famously won a court case against Hastings' St John's College after being suspended for refusing to cut his long locks.

The High Court ruled that the decision to suspend him was unlawful and the school's rule over hair length was vague and uncertain.