The I.R.S. almost never audits private equity firms, even as whistle-blowers have filed claims alleging illegal tax avoidance. : The I.R.S. almost never audits private equity firms, even as whistle-blowers have filed claims alleging illegal tax avoidance. There were two weeks left in the Trump administration when the Treasury Department handed down a set of rules governing an obscure corner of the tax code. Overseen by a senior Treasury official whose previous job involved helping the wealthy avoid taxes, the new regulations represented a major victory for private equity firms.