A batch of 240 letters sent by a Columbia University business professor in a bid to teach students how companies handle complaints, has landed him in hot water.

Six restaurateurs are now suing the university for US$100m, claiming the study was libelous, “unethical and malicious”.

Last August, Francis J. Flynn, an assistant business professor, sent out the letters to New York restaurants falsely complaining of food poisoning as part of a project judging how businesses respond to complaints.

Flynn claimed he had visited the restaurant for a meal with his wife on their wedding anniversary, after which he suffered “extended nausea, vomiting, diarrhoea and abdominal cramps”.

Despite not being authorised by the university, the letters were on official Columbia stationery and caused serious concern amongst restaurant staff, who scoured credit card records, menus and delivery tickets to establish when Flynn might have visited and what the possible causes of the poisoning could have been.

Virgil Renzulli, Columbia’s associate VP for public affairs, told the Associated Press that the business school sent written apologies to all 240 restaurants when the project was exposed in September.