Waka Kotahi the New Zealand Transport Agency, which works within legislation, says what is permitted on traffic signs is "quite limited in terms of wording and symbols" and any changes would need to go through the Transport Ministry.
It comes as the issue of bilingual city entrance signs was raised at a Rotorua Lakes Council Operations and Monitoring Committee meeting on Thursday last week.
In the meeting, councillor Raj Kumar said he understood there had been moves to introduce bilingual signage at the entranceways to Rotorua but NZTA had "objected".
Council manahautū Māori (Māori manager) Gina Rangi said there was a problem with NZTA's regulations.
"I've been very clear [to Waka Kotahi] that their regulations need to be updated to allow for high-quality te reo Māori signage.
"Some of their standard accepted translations are not high quality or they're not accurate, and then in other places they don't allow any translations at all ... but that's something that sits with NZTA, we can only lobby them."
On Monday, Rangi clarified her statements, saying in 2018 the council went through "some months" of negotiation with the transport agency to introduce entrance signs near Hemo Gorge that included te reo Māori, but it was "initially rejected" by the agency.
"The process highlighted that Waka Kotahi regulations do not allow for Māori language as a recognised, standard option for common signs, including entranceway signage."
She said another example was that Kura Kaupapa Māori were unable to use Māori language signs for their traffic patrols as the regulations required that they must use English.
In the meeting, councillor Merepeka Raukawa-Tait said the council should not "let it lie", but lobby for a precedent for bilingual signage.
Rotorua Mayor Steve Chadwick agreed.
"One of their arguments that I didn't find legitimate was if you were trying to put bilingual wording [on signs] you cluttered up the sign and people might bang into it, which was rather stupid.
"I think we can have another go at it with a new minister."
On November 6, Michael Wood was sworn in as the new Transport Minister, replacing Phil Twyford.
In August 2017, Te Tatau o Te Arawa, the council and Te Puni Kōkiri announced Rotorua to be the first bilingual city in New Zealand, which has been described as an effort to support and promote both te reo Māori and English.
A Waka Kotahi spokeswoman said current regulations permitted "guide signs, tourist signs and general interest signs" to have bilingual destinations if approved by the New Zealand Geographic Board.
"The issues in question in Rotorua specifically relate to the signs identified needing to serve as an effective and legally enforceable speed limit sign."
The layout and content of traffic signs was governed by the Traffic Control Devices rule, which was made in accordance with the Land Transport Act 1998.
Speed limit signs had both a safety and regulatory function and that could not be compromised or invalidated, the spokeswoman said.
Waka Kotahi had worked with the council to install a te reo Māori version of the speed threshold sign installed on one side of the road "and the legally complying English version on the other side".
The spokeswoman said Waka Kotahi developed two options for paired use for entryway speed limit signs that councils could use nationally. They were "nau mai ki" or "haere mai ki", and Rotorua had selected the first option.
There were speed limit threshold signs using both options in other locations, she said.
The spokeswoman said there were other ways to "display or promote" te reo Māori than traffic signs that were "potentially far more useful, given they can be larger … and less restrictive".
The agency was exploring how to build the "capability and the evidence base" for introducing bilingual transport signage by considering the likely impacts of bilingual signage on road safety, what could be learned from international examples, and questions of consistency.
"We will then work with the Ministry of Transport and the wider sector to develop and deliver a sector-wide outcome. This may require an amendment to the current Traffic Control Devices Rule."
Waru said on Monday Waka Kotahi NZTA's regulations needed a "big review" so that te reo Māori had "the same mana as te reo Pākehā - English".
He described the idea of only English signs being legally compliant had "a touch of racism".
He called on incoming Transport Minister Michael Wood to fix the rules.
The Rotorua Daily Post asked Wood his views on the rules, whether he agreed with Waru and whether he would undertake a review into them.
Wood said Waka Kotahi was "on a journey to embrace and promote te reo Māori".
"They're making progress and I'm certainly happy to consider any advice the Ministry [of Transport] provides on how to boost te reo on our roads further."
In response to Waru's comments, the Waka Kotahi spokeswoman said the organisation "respects and values the importance of te reo Māori as one of our country's official languages" and was keen to consider how te reo Māori was represented in its work, which included "working with local councils to incorporate bilingual road signage, while achieving safety outcomes".