Traditional Owners and the Australian Conservation Foundation, united in opposition to a proposed radioactive waste facility in regional South Australia, are alarmed that preliminary earthworks have begun at the site before the conclusion of a Federal Court challenge to the dump plan.

Barngarla Native Title holders are contesting the validity of the former federal government's selection of the site, at Napandee, near Kimba on the Eyre Peninsula, in court.

The ACF described the earthworks, which Federal Resources Minister Madeleine King has confirmed, as "pre-emptive and unjustified".

ACF First Nations lead Josie Alec said the aim of the Foundation is to support the Traditional Owners in their challenge to the plan.

"This whole project has not been backed by anyone except the guys who will make a profit from it," she said.

"This was approved by the last federal government, there was no procedural fairness, fair process has not been put in play. As far as consultation with the mob goes their right to veto has not been considered at all.

"Our role is to support the Traditional Owners having a voice and free prior and informed consent. If this project goes ahead, it will be an environmental disaster."

South Australian Premier Peter Malinauskas has backed the Barngarla Native Title holders' right to veto the project and in October the SA Labor state convention found that the waste plan "undermines efforts toward reconciliation".

The ACF said Eyre Peninsula grain producers and Unions SA, and a range of other groups, had rallied to support the Barngarla people in their stance.

Foundation campaigner Dave Sweeney said the federal government had "inherited a divisive and deficient approach to radioactive waste management" from the Morrison government.

"The plan is not responsible, necessary or consistent with international best practice or Labor's stated values and platform," he said.

"The decision to commence site works is a poor one, but not an irreversible one."

A spokesperson for federal Resources Minister Madeleine King said the facility will help "fulfil Australia's obligation to responsibly manage its own radioactive waste, most of which comes from making nuclear medicine".

"ARWA (Australian Radioactive Waste Agency) is now starting preliminary site characterisation activities on and around the site we acquired. The activities are not being done in preparation for construction to commence," they said.

The spokesperson said the works are reversible and will help ARWA obtain more detailed information on the site to inform design work.

"And importantly, cultural heritage on the site will be protected by a Cultural Heritage Management Plan," they said.