Chevron is defending itself against what it says are false allegations that it is responsible for alleged environmental and social harms in the Amazon region of Ecuador.
Stone cited health problems for being a no-show at gigs scheduled for April last year where she was slated to be the latest high-profile celeb to have condemned Chevron, and is being sued in a federal law suit in New York for $US352,000 ($A450,840).
MCSquared also paid Lethal Weapon 1980s star Danny Glover and legendary director Woody Allen's ex-wife, actress Mia Farrow to attend the events last year, the latter of whom admitted to being paid by agents of the Ecuadorian government to travel there to support its legal and political battle against Chevron.
"They paid my speaking fee - nowhere near that amount," she tweeted on September 17 in response to a Washington Free Beacon report revealing MCSquared PR paid her agency $188,000 in 2013.
"I wouldn't have gone if I didn't believe in the cause."
The newspaper said the firm also paid Glover $330,000, with the celeb pair touring areas of the rainforest allegedly contaminated by Texaco, which Chevron acquired in 2001.
The Brooklyn-based PR firm alleges Stone failed to return a $275,000 fee that Boston firm American Program Bureau paid her.
MCSquared also said it spent $77,420 "to accommodate Stone's diva-like requests, including first-class airfare tickets and luxury hotel suites for herself and her three companions," along with hair and makeup services and personal guides.
While analysts believe Ecuador's rainforest was almost certainly scarred by previous hydrocarbon activity, the antics of MCSquared have given Chevron leverage to deflect the blame.
Protesters at Chevron's annual shareholder meeting last May were paid $85 to wave placards and shout slogans, with a Los Angeles film production company admitting it recruited them - though it's unclear who got the production company to do it.
"The fact that the Republic of Ecuador's PR firm is suing Sharon Stone for not participating in a government-sponsored anti-Chevron stunt is further evidence that this case is nothing but a fraud," Chevron spokesman Morgan Crinklaw told Bloomberg in an e-mail.
"From paid celebrities to bribed court officials to the ghost-written judgment, the case against Chevron in Ecuador is a well-funded and manufactured extortion scheme."
In February 2011, an $18 billion judgment - later reduced to $9.5 billion - was rendered against Chevron by a court in Lago Agrio, Ecuador, for alleged contamination resulting from crude oil production in the region.
On March 4 last year the US District Court for New York's Southern District ruled the $9.5 billion Ecuadorian judgment against Chevron was the product of fraud and racketeering activity, finding it unenforceable.
The nearly 500-page ruling found Steven Donziger, the lead American lawyer behind the Ecuadorian lawsuit against the company, violated the federal Racketeer Influenced and Corrupt Organizations Act, committing extortion, money laundering, wire fraud, Foreign Corrupt Practices Act violations, witness tampering and obstruction of justice in obtaining the Ecuadorian judgment and in trying to cover up his and his associates' crimes.
The ruling prohibits Donziger and his associates from seeking to enforce the Ecuadorian judgment in the United States and further prohibits them from profiting from their illegal acts.
