Rio Tinto's relationship with an indigenous group in Kakadu National Park has taken "two steps backward" after a safety breach at the Ranger uranium mine.
The Rio subsidiary that operates Ranger, Energy Resources of Australia, has confirmed that a vehicle used within the mine was taken out of controlled areas, sparking contamination fears among the nearby Mirrar people.
Police are investigating the incident, which took place without the consent of ERA management in the early hours of Sunday morning, and which some believe may be a breach of the company's authorisation to mine.
Like all uranium mines, Ranger operates under strict conditions to ensure dangerous levels of uranium do not contaminate the nearby area.
ERA said the car - which was supposed to remain inside the mine at all times - had been checked and was "free of contamination".
But Justin O'Brien, who represents the Mirrar people, said it had caused great concern among the local community.
"We think it is very serious that you could take potentially contaminated material from an operational mine site, avoid all scrutiny, leave the mine site with it and then be found down the highway," he said. "There needs to be a broader inquiry into how on earth this could happen in the first place."
ERA's relationship with the Mirrar people is crucial to its survival, given the company has agreed not to restart mining at Ranger without approval from the group.
Ranger ceased operating as an open-cut mine last year, and its only future lies in winning approval to become an underground mine in coming years.
The nearby Jabiluka uranium deposit will also not be mined until the Mirrar people give their full support, something that appears unlikely any time soon.
The Mirrar people had recently spoken of their improving relationship with ERA and Rio, which was given a boost in September when ERA installed a $220 million water purification system on site.
But Mr O'Brien said incidents like the one at the weekend did not help Rio's chances of winning further approvals to mine.
"It can only stress the relationship, it can only challenge the relationship and the test is how the company responds to this in terms of its management of the investigation and its response with the contractor," he said.
Australian Conservation Foundation spokesman Dave Sweeney said it was not the first breach at Ranger, and it was time for Rio Tinto to "reconsider the project".