Unregistered raw milk suppliers around the country have been banned from selling their product.
The purchase follows MPI's introduction of a new mobile x-ray last year to screen the bags of cruise ship passengers arriving at North Island ports.
"The additional mobile units give MPI greater flexibility to wheel out x-ray screening for fresh fruit and other biosecurity goods across the whole country," says MPI detection technology manager Brett Hickman.
"This year their use won't be restricted to cruise ship passengers. They'll go to where the action is.
'For example, they will provide backup for our fixed biosecurity x-ray units at airports and Auckland’s International Mail Centre.
"We've already used one to scan international mail items while an existing permanent x-ray machine was undergoing repairs."
He also expects to see them used for screening express freight items and if for any reason MPI needed to set up a special biosecurity clearance area.
One of the mobile units is due to head to its base in Tauranga this week. The other two units will be based in Auckland and Dunedin.
"We'll be able to deploy the machines from these bases at short notice to wherever they are required," says Hickman.
MPI currently owns and operates 28 fixed x-ray units for baggage scanning at international airports, military bases and the Auckland International Mail Centre.