A former Walt Disney Co. accountant has accused the company of overstating revenue for years and has filed a series of whistleblower tips with the U.S. Securities and Exchange Commission.

Sandra Kuba, previously a senior financial analyst who worked for Disney for 18 years, said employees in the parks division systematically overstated revenue by billions of dollars, according to MarketWatch, which said it reviewed the filings.

Disney (DIS) denied the claims in statement to the news service. The company didn’t respond to a request for comment from Bloomberg. Judy Burns, an SEC spokeswoman, declined to comment.

The report rattled investors, who sent the shares lower after they’d been up as much as 1.8%. They were little changed at the close in New York.

Kuba’s filings said employees sometimes recorded sales twice for gift cards, when guests purchased a card and when they were used. Revenue was counted even when a card was given to a guest following a complaint, according to MarketWatch. Kuba’s filing alleges that flaws in the accounting software made the manipulation hard to trace.

She said 2008-09 revenue may have been overstated by up to $6 billion.