The two companies manufacture a range of munitions at the plants, which are used by police and the Australian Defence Force.
Protestors were sitting at the entrance to the site with a brightly painted vehicle and an improvised fence.
A NIOA spokesperson said the protest had not caused any disruptions to its Benalla operations.
Protest organisers said about 25 protestors were occupying the road between the blockade and the factory gates.
The protestors were calling for Australian police to be disarmed, and maintain that “NIOA profits from police violence”.
Banners read ‘Disarm Police’, ‘Ceasefire’ and ‘Karrinjarla Muwajarri’.
This is the second time the group has blockaded NIOA’s factory in connection with a Yuendumu Elders’ campaign to keep police guns out of communities after the shooting death of Kumanjayi Walker.
The protestors have also set up a memorial to a number of West Papuan civilians killed by the Indonesian military and police since 2021.
“Weapons corporations like NIOA and Thales are making a killing taking black lives, while driving dispossession and enforcing ecocide across our region,” group spokesperson Zelda Grimshaw said.
“It is past time to put peace and climate justice ahead of the profits of arms manufacturers.
“We don’t need a billion bullets. We need our children alive, and a planet they can thrive on. We are calling for earth care, not warfare.”
Thales has also been contacted for comment.