Northern Dynasty president and CEO Ronald Thiessen said the only way to stop Pebble was by federal govenrment expropriation - extremely difficult since the deposit was on state lands.

The company scored a critical victory last month when it received a positive environmental impact statement for its proposed Pebble copper-gold-molybdenum project from the US Army Corps of Engineers.

However, opposition to Pebble seems to be building across partisan lines with Donald Trump Jr recently voicing opposition to the project, and Trump senior initiating a White House review of the EIS decision. It remains unclear what a negative outcome from such a review would mean for the permit, with a record of decision expected to be published in the federal register by mid-September.

Thiessen insists the EIS is the final word on federal permitting of the project. State permitting is ongoing as and when design and construction proceeds.

"If Mr Biden wins the presidency he will have to adhere to statute. He cannot simply bypass statute through executive orders and even if he does, his decision would have to be backed up by a record of due process, in other words, another environmental impact study, otherwise his decision will be overturned by the relevant authority, in this case the EPA," he said.

"The RoD will have been issued by the election, and so any attempt by a Biden presidency at that time to withdraw that permit is without statutory authority and therefore, either an administrative or judicial review would overturn that decision. Really his only way of stopping it is an expropriation.

"I just don't think we'll go there."

PLP CEO Tom Collier said this week prior efforts by the Obama administration to impose regulatory decisions at Pebble without an EIS or other legally defensible administrative record were stopped by the courts, and any similar action would be met with the same fate.

"Any suggestion that the Obama-era Bristol Bay Watershed Assessment (BBWA) is a more defensible administrative record for regulatory decision-making at Pebble than the final EIS is laughable," he said.

"Not only does the BBWA not even assess our project, it doesn't consider project-specific mitigation, it's based almost entirely on secondary research, and it isn't an impact assessment. As a basis for regulatory decision-making, the BBWA is woefully inadequate and demonstrably inferior to the final EIS, and I'm 100% certain that our federal courts will take the same view if they are asked."

Collier echoed Thiessen in saying any action by a Democratic administration to challenge federal permits once granted would have "severe negative implications" for the country's reputation as a jurisdiction for business investment.