Other restrictions include not being able to take milk to businesses, because, according to Mr Lethbridge, "MPI is worried about milk getting warm on the way home". He added the same rules don't appear to apply to people buying meat from butchers or supermarkets.
"I believe MPI set out to stop us from trading and that's what they have achieved," said a very annoyed Mr Lethbridge.
He started trading on October 1 last year in response to falling global dairy prices, growing the business to return up to $1500 a week - a welcome addition to the farm income, when the global milk market continues to seek new lows.
Mr Lethbridge was selling up to 450 one- or two-litre bottles of whole milk a week. He bought a refrigerated truck and had recently moved into the Auckland market - mainly around Warkworth and Whangaparaoa - and says there has been "huge" response from many of his customers to him closing the business.
His customers include people who use his milk to make cheeses or yoghurt.
"Many have told me they don't want to go back to pasteurised or homogenised."
Mr Lethbridge milks 400 cows and is a Fonterra supplier - he is one of the few dairy farmers in the region to achieve no grades (milk contamination) this season.
MPI's testing regime is another source of irritation as his milk hygiene is demonstrably exemplary.
"It's quite a big deal to be grade free this season, because of the high rainfall - but that doesn't mean anything to MPI, we still have to test to their specifications.
"I'm very disappointed that MPI is forcing raw milk producers out of the market - the product is great and there's a big demand for it."
And the timing of ending the operation couldn't be much worse - he had just bought 3000 glass bottles (imported from Germany) which he's now going to put on Trade Me.