Several hundred farmers have gathered to protest against a water tax in Labour leader Jacinda Ardern's home town of Morrinsville, with the protest turning sour when NZ First's Winston Peters turned up.

The protesters say farmers are being unfairly targeted with Labour's proposed water tax of 1 or 2 cents per 1000 litres of irrigated water.

"Us dairy farmers, we have been taking a pounding from New Zealand politicians and our interests and values are at stake," Michelle Wilson from Waihi told the crowd through a loudhailer.

Bob Appleton, who came to the protest onboard tractor 'Myrtle', said he's paid $40,000 towards riparian planting over the past four years and has fenced off all his streams.

"I honestly think they [Labour] buy their food from the supermarket," Mr Appleton said.

"They don't listen to us farmers. We, I think, are the guts of the country. We've got too computerised, and we're an agriculture country, and this water tax thing's stupid."