Heirs of art dealer Ileana Sonnabend, who died in 2007, are in a bind for inheriting a 20th-century masterwork by Robert Rauschenberg.

Next month lawyers for the heirs will go head to head with the Internal Revenue Service over the value of Rauschenberg's "Canyon."

The artwork, comprised of assembled and found objects, features a stuffed bald eagle. Under federal law, the eagle can not be sold. Sonnabend's heirs have had the work appraised at zero value for tax purposes.

An art advisory panel for the IRS claims the fair market value of "Canyon" is $65 million. A tax bill of $29 million was sent to the heirs plus penalties of $11.7 million will need to be paid if they lose the fight.

The heirs refused to pay the tax bill on the eagle artwork, but they have paid $471 million in federal and state estate taxes related to Sonnabend’s nearly $1 billion art collection. Works have also been sold for approximately $600 million to pay the taxes they owed.

In Washington, lawyers will argue in tax court over the sky-high tax bill for an artwork that is illegal to sell. Currently, "Canyons" is on loan to the Metropolitan Museum of Art.