Reports show Charity Investment Asset Management (CIAM), a French hedge fund, said Walt Disney scooped €930m (£780m) in royalties allowing Euro Disney to use characters like Mickey Mouse at a rate at least three times the standard market practice.
CIAM has taken the company to French criminal courts for misuse of corporate assets, publication of inaccurate accounts and misleading information, while fighting a second civil case for shareholders to be reimbursed the nearly €1bn of overpaid fees.
The firm has also said Walt Disney hid the value of 5,000 acres of land around Paris which Euro Disney is developing. Walt Disney offered €1.25 a share, but CIAM said the land was independently valued at €1.9bn, which works out to €2.40 a share.
The struggling theme park had a particularly tough year as terrorist attacks in Paris caused tourism figures to slump. It lost €858m in the year to September 30.
Walt Disney said the action was "utterly without merit".
The animated cartoon creator doubled its stake to 77 per cent last year after a debt-for-equity swap was approved by French officials.
Shares in the company have lost more than 90 per cent of their value since the company went public in 1989.
CIAM's co-founder Anne-Sophie d'Andlau said the firm thinks Walt Disney plans to take Euro Disney out of the market without properly valuing the company.