Lawyers for New York attorney Steven Donziger and a group of Ecuadorean environmental plaintiffs reloaded this week in their epic fight with Chevron Corporation, asking an appeals court to vacate a finding that Donziger procured a $9.5 billion judgment against the oil giant through wholesale fraud.

Donziger’s prominent appellate lawyer, Deepak Gupta of Gupta Beck, filed a 136-page opening brief for his embattled client late Wednesday at the U.S. Court of Appeals for the Second Circuit. Gupta urged the court to rule that U.S. District Judge Lewis Kaplan overstepped his authority and ignored key evidence when he concluded in March that the Ecuadorean judgment against Chevron was fatally tainted by judicial bribery and other misconduct involving Donziger. Kaplan’s ruling was viewed as a critical step in Chevron’s campaign to block the Ecuadoreans from collecting on their judgment worldwide.