Fortune has been looking into whether one of the nation’s top mutual companies has been avoiding taxes in a recent article that examines the Vanguard whistleblower saga that has been developing for almost two years now.

The mutual fund giant, known for its low cost index funds, might soon have to pay billions of dollars more in fees each year if the whistleblower suit submitted by a former employee proves to have merit.

The suit states that Vanguard owes the state close to $35 billion in taxes, penalties, and interest over the last eight years. While the fund’s investors would not have to cover those payments, Vanguard could potentially have to raise its standard fees dramatically, with some estimates citing as high as four times their current levels in order to comply with tax laws. This would increase the amount paid by investors in fees by around $20 billion a year.

However, Fortune says, therein lays the problem. “Vanguard is set up like a mutually owned company to benefit investors in its funds. Vanguard says the fees it charges its mutual funds investors are “at cost.” Other mutual funds companies charge their investors a fee equal to the amount it costs to run the fund plus a mark-up for a profit. The ‘at cost’ arrangement essentially allows Vanguard, which is a private, for-profit company according to the suit to claim it its mutual funds owe no taxes because all the benefits go to its investors.”

If put in the position where it would have to pay the taxes the suit alleges it avoids, and truly keep the service at cost, Vanguard would have to raise its fees enough to cover all the fees it is currently ‘avoiding’. This could present a problem for the company as its main draw is exactly those low fees it charges for its funds.

However, Vanguard itself states that any talk about rising of its fees is “speculative”, and that its mutual funds pay a “fair and appropriate amount of taxes.”