Opponents of this bill link it to Codex Alimentarius, and predict that all governments will attempt to implement it, unless they are resisted. Readers are free to google the actual terms of Codex, everything is in plain view. A critical analysis of Codex is here. The agreements regulates food and nutrients and can be enforced by the World Trade Organisation. Everything that people eat must meet the specifications of the authorities. The New Zealand Bill codifies this into a national law, and it seems natural to assume that other governments will want to follow.
The US has seen raids on farms in recent times, in federal actions that seem anything but even-handed. More here.
There seem to be numerous parallels between restrictions on freedom to grow food and restrictions on smoking. Both are done ostensibly in the of safety, both seek to undermine if not actually people's own views about what constitutes safe consumption. Under both food safety and non-smoking regimes the wrongs perpetrated by relevant mega-corporations are ignored while the small farmer/smoker comes under intense scrutiny without being adequate means to oppose the government's arguments. In each case the mega corporation bravely takes on the small trader.
That said, this area is new to me. I'm reserving further comment until I have read more on this.