Rio is building a giant underground copper mine, known as Oyu Tolgoi, in the country. Yet the project has been beset by delays, legal probes, cost overruns and government pressure.

Rio said Tuesday that early reports suggest an administrative court has upheld claims by the Darkhan Mongol Nogoon Negdel non-governmental organization that Mongolia didn’t follow due process on the agreement that underpins its development of the asset.

The group, which promotes ecological balance and economic independence, had disputed the Dubai agreement signed in 2015, as well as the authority of Mongolian government officials involved in the negotiations.

It’s not yet clear what the implications will be. But with the court’s formal written ruling expected to be released in the coming weeks, it adds a fresh element of uncertainty to an already difficult project.

“The Dubai agreement is not annulled by the court decision. However, this decision raises questions about due authorization and capacity of those who signed the Dubai agreement,” said lawyer Solongoo Bayarsaikhan, a managing partner of Avinex Partners LLP in the capital, Ulaanbaatar, who is not involved in the case. “We need to see the actual court decision.”

Earlier this year, Rio warned that its flagship growth project could cost as much as $1.9 billion more than forecast and faces potential delays to full production of as long as two and a half years. The expansion of the mine has run into difficulties after potential stability risks were identified within the planned underground operation, and it could now cost as much as $7.2 billion.

The overruns will mean Mongolia must wait longer before profits start flowing from the mine to the government.

On top of the actual problems building the project, there have been numerous controversies in the country. A parliamentary working group recommended in April that Mongolia review the 2009 deal that launched construction and revoke a 2015 agreement allowing for an underground expansion to tap into most of its mineral wealth. The mine has also been at the center of tax disputes and a probe into allegations of corruption.

Rio said that it “strongly refutes” any suggestion that its agreement is illegal.

To contact the reporters on this story: Thomas Biesheuvel in London at tbiesheuvel@bloomberg.net;Terrence Edwards in Ulaanbaatar at tedwards100@bloomberg.net

To contact the editors responsible for this story: Lynn Thomasson at lthomasson@bloomberg.net, Liezel Hill, Dylan Griffiths