They were marching against the Registration of Land and Titles Act of 2008, which requires the registration of public land, freehold land, and customary leases and licences.
Critics say the law violates customary land rights by breaking communal land into individual - private - titles.
A paramount chief, lawyer, and former opposition politician, Leota Su'atele Manusegi, who was at the protest, says the law opens land for sale and exploitation.