The estate of the late William Davidson is taking the IRS to court in what could be one of the largest cases of its kind, with representatives of the Bloomfield Hills billionaire claiming the agency is wrongly trying to squeeze nearly $2 billion in taxes out of the estate — if not more. Late last week, the estate’s lawyers filed a petition in U.S. Tax Court in Washington, D.C., arguing that an IRS notice in May wrongly claimed $2.8 billion of underpayments in estate taxes, gift taxes, penalties and more. While it’s unlikely the entire amount would be owed the government, a tax bill of nearly $2 billion is not out of the question. In contrast, the Davidson estate’s lawyers argue, not a dime more than has already been paid is owed the IRS, setting the stage for what could be a protracted legal battle involving the legacy of Davidson, who Forbes called the 62nd-richest man in the U.S. in 2008, with a net worth of $5.5 billion. “It’s huge,” said Beth Kaufman, a trusts and estate lawyer at Caplin & Drysdale in Washington, who is not involved in the case. “Just the sheer dollar amounts involved here are enormous.” While the issues involved — how much certain assets were worth, and the amount owed, if any, on swaps made to trusts for Davidson’s children or grandchildren — are somewhat routine, Kaufman said it’s the size of what the IRS cites as deficiencies in its notice of May 2 that puts this case in a different stratosphere. Ron Aucutt, the head of private wealth services at the McGuireWoods law firm’s northern Virginia office, agreed. “Clearly when you see a number with that many digits in it you usually think big oil company or huge financial institution,” he said. “Not an individual.” The IRS declined to comment, citing rules on tax determinations and litigation, and no statistics on the relative size of the petition were available. But the estate tax alone — $1.9 billion — would represent more than one-tenth of the $13 billion collected through that tax nationwide in 2010, when taxes on most estates of those who died in 2009, like Davidson, were paid. It’s not the first time Davidson’s estate and heirs have been in the news: In May, records unsealed in Oakland County Probate Court at the Free Press’ request showed his relatives feuding over who should control his Southfield-based charitable trust, though that battle is now expected to play out in Delaware, where the foundation is incorporated.