Woodside Energy has accused a United States government department of showing bias and hostility toward oil and gas producers in a lawsuit that claims it and other companies were wrongly charged billions of dollars worth of excess royalties.

The dispute between Australia’s biggest oil company and the US Department of Interior is playing out across two cases in the Louisiana District Court, in which Woodside said a trove of “compromising emails” showed departmental staff used underhand tactics to try to make the company overpay.