The Pebble Limited Partnership and former CEO Tom Collier have each been served with a subpoena to provide documents in connection with a grand jury investigation that is currently under way.
The investigation involves previously disclosed recordings of private conversations regarding the contentious Pebble project, in Alaska.
Canada’s Northern Dynasty said its US subsidiary and Collier would cooperate with the investigation.
Collier resigned in September after his comments on elected and regulatory officials in the US were covertly videotaped and released by an environmental activist group. In the tapes, Collier and other mining executives discussed their influence over Republican Governor Mike Dunleavy and Alaskan politicians.
In the conversations, company officials also suggested that while they were seeking a permit for a 20-year operation, Pebble might expand for as long as 180 years.
The US Army Corps of Engineers in November denied a key water permit for the Pebble mine, putting the future of the project in doubt. The company and the state of Alaska have filed an appeal.