Dairy farming was initially rated as one of the highest-risk industries during health and safety reforms before the Labour Minister, Michael Woodhouse, intervened and changed the criteria, documents show.
Under fiercely-debated law changes in August, "high-risk" businesses cannot be exempted from a key requirement to have a health and safety representative if a worker requests one, even if they have fewer than 20 employees.
Documents released under the Official Information Act reveal the process for determining which industries would be classed as high-risk.
In the first list produced by Worksafe officials for the minister, which was based on the industry standard ANZSIC Level 2 figures, agriculture was in the highest category.
In a more detailed list, based on ANZSIC Level 3 figures, "dairy cattle farming" was rated in the second-highest category, which meant workers were exposed to levels of risk "greater than twice the average and up to three times the average (for severe injury), or up to four times the average (for fatality)".
Two weeks later, Mr Woodhouse's private secretary sent an email to officials with new criteria for the "high-risk" category and a list of industries. It did not include dairy farming. An official replied to Mr Woodhouse late that evening, saying that it was "important to flag that the application of the criteria ... has the following effects (at least some of which may be unintended)".
The official said fewer than 4 per cent of small agriculture businesses would be able to request a health and safety representative. They also warned that the high-risk category would include worm farmers and merry-go-round operators.
Mr Woodhouse rejected suggestions he had deliberately excluded the dairy industry. "People are perceiving this to be letting the farmers off the hook. But ... the new legislation provides much more expectations on everybody to participate in health and safety," he said.
Labour's workplace safety spokesman, Iain Lees-Galloway, said it appeared the criteria had been finely tuned to "exclude agriculture".
10 Feb: Minister proposes businesses with 6 or more workers will maintain ability to nominate a health and safety representative, if a worker requests one.
24 July: Threshold for nominating health and safety rep increased to 20 or more workers, except for the high-risk industries.
Aug 7: First list of high-risk industries presented to minister, which includes agriculture.
Aug 17: Minister asks for new criteria, and provides a list which excludes dairy farming but includes share-milking.