The federal customs administration has opened an investigation into Urs E. Schwarzenbach, owner of the five-star establishment, customs spokesman Oliver Brand told the ATS news agency.
Custom agents conducted a search of the hotel, perched on the hills overlooking Zurich, on April 16th, Brand said, confirming information published on Sunday by the SonntagsZeitung and Matin Dimanche newspapers.
The investigation also concerns an art gallery, ATS said.
Brand declined to provide additional information because the inquiry remains under way.
The probe should be wrapped up by the second half of next year, ATS reported.
Schwarzenbach, a Swiss-born hotelier and financier with a fortune estimated between €1.5 billion and €2 billion ($2 billion and $2.75 billion), is reportedly based in England.
British media have described him as a polo-playing friend of Prince Charles who purchased an entire village — Hambledon in Buckinghamshire — for a reputed £38 million ($64 million) six years ago.
Swiss media reported that he lent his stables in Herrliberg (in the canton of Zurich) to Steve Guerdat, the Swiss Olympic equestrian champion.