WELLINGTON, New Zealand — Tens of thousands of New Zealanders rallied in front of Parliament on Tuesday in one of the country’s largest ever protests to oppose a bill, which opponents say seeks to dilute the rights of Maori and threatens to set race relations back decades.

Massive crowds estimated by the police at 42,000 gathered at Parliament, where the Treaty Principles Bill was introduced earlier this month by legislators who want to reinterpret a 184-year-old treaty signed between the British and Indigenous Maori.

While the bill lacks enough support to pass, critics see in it a desire to reverse decades of policies that aimed to empower Maori, who make up around 20% of the 5.3 million population but have higher levels of deprivation and incarceration and worse health outcomes than the broader population.

“I’m here for my grandchildren, my children and for their children,” said Hoana Hadfield from Wellington, who was marching in a protest for the first time.

“I think it’s important that we keep our kaupapa, which is our values as Maori and our culture, and it’s a real big thing for us to have cultural identity.”

Some people in the crowd were dressed in traditional attire with feathered headgear and cloaks and carried traditional Maori weapons, while others wore T-shirts emblazoned with Toitu te Tiriti (Honor the Treaty). Hundreds carried the Maori national flag.

The protest was preceded by a nine-day march, or hikoi, that began in the country’s far north, with thousands joining rallies in towns and cities as marchers traveled south on foot and in cars to Wellington.

Unity and solidarity was spoken about a lot in the rally. Helmut Modlik, a leader in the Ngati Toa tribe, told the crowd that it was too late to divide the country.

“To those who will divide us, whanau, it is too late. We are already one people,” Modlik said to cheers from those gathered on the lawns of Parliament.