When I teach Federal Income Tax, I always describe to my students the broad powers of the IRS to request and inspect records during an audit. It is not uncommon for the IRS to meet with the taxpayer in the taxpayer's home or on the taxpayer's business premises. Although the IRS typically contacts a taxpayer by mail first, surprise in-person visits may happen, as explained by the IRS here, in cases of "an overdue tax bill, to secure a delinquent tax return or a delinquent employment tax payment, or to tour a business as part of an audit or during criminal investigations." I half-jokingly tell my students not to be surprised if the IRS wants to look in the taxpayer's dresser drawers.
Until today, though, I've never heard of an IRS agent following a taxpayer to the bathroom and monitoring the taxpayer's ... um... use of the facilities. Today in Ioane v. Hodges (here), the Ninth Circuit ruled that an IRS agent cannot invoke a qualified immunity defense in a case in which the agent allegedly "violated plaintiff’s Fourth Amendment right to bodily privacy when, during the lawful execution of a search warrant at plaintiff’s home, the agent escorted plaintiff to the bathroom and monitored her while she relieved herself."
I don't see a circuit split on this one, and it's doubtful the IRS will appeal. I predict that SCOTUS will not be taking on this particular aspect of the jurisprudence of toilets any time soon.
Image source: Science, Industry and Business Library: General Collection , The New York Public Library. "Visiting-inspectors building ; Toilet for foremen ; North gatehouse ; A shop toilet ; Changehouse locker-room." New York Public Library Digital Collections.