Fonterra general manager of national transport and logistics Barry McColl said the company would try to get drivers to lose weight so they could get back on the roads, or they could change their roles in the company.

Fonterra truck drivers are being told they are at risk behind the wheel because of their weight.

Drivers who weigh more than 150kgs were told this week to step down from driving in light of revelations seats could not accommodate their weight safely.

A "health and wellness" programme was being tailored to those who wished to continue driving.

MARION VAN DIJK/STUFF Fonterra trucks have always been risky for heavier drivers, management has discovered.

Fonterra general manager of national transport logistics Barry McColl said discussions with manufacturers about getting larger seatbelts in trucks revealed there was a "risk safety features would not perform to the design standard" if drivers were above 150kg in some trucks and 140kg in others.

McColl said about 50 drivers were in the "150kg-plus range".

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Truck seatbelts are mounted to the seat instead of the vehicle frame, as they are in cars, which increased the possibility they could detach in the event of an accident, he said.

It also increased the risk a seat could deform or detach in an accident, he said.

The two models of trucks that are used to carry milk tankers for the company are Scania and Volvo brands.

McColl said the weight limit on Scania trucks was 140kg, and 150kg in Volvo brand trucks.

McColl said individual conversations were had with truck drivers to work on a health management plan and assign them "alternative duties" until they could meet a safe weight.

"First and foremost protect the employee and work to get them to a point where they can be back on the road, or if that's not possible we'll reassign them work packing or processing and there is potential to upskill them within those roles."

McColl said there was no intention that the drivers would be "parting company".

"It's a very delicate conversation to have...from a safety point of view you can't put them in a situation where they are at a higher level of risk than other drivers."

McColl said Fonterra was working with the Dairy Workers Union to partner with drivers on wellness plans and do a country-wide roll out of those in the next couple of weeks.

Employment lawyer Max Whitehead said he first heard about the policy from a colleague of an affected truck driver who weighed 150kg and had worked for the company for seven years.

Whitehead said Fonterra was "directing its New Zealand managers to blatantly discriminate" and the policy was "grossly unfair and in breach of New Zealand law".

McColl denied that it was a case of discrimination, and said it was "purely and simply you are putting them in an unsafe situation if they were to get in an accident".

A Fonterra spokesman said that Whitehead had not contacted the company.