Hoteliers said they have racked up huge bills after being asked to send information to companies promising to promote them.
They said they did not know that the 090 numbers they were calling charged them around £1 per minute.
Now the body which regulates premium rate services has warned those working in hotels and guest houses to be on their guard.
Services offered
And its message has been backed by the vice-chairman of the Argyll, the Isles, Loch Lomond, Stirling and Trossachs Tourist Board, who said he has been targeted three times.
A handful of companies have been offering, or claiming to offer, accommodation and corporate services to hoteliers.
Hotel staff were asked to fax information such as brochures, maps or menus through to an 090 number - and, contrary to regulations, received no indication they would be charged at premium rates.
The hotels were often asked to supply as much literature as possible, extending the length of the call and making more money for the companies - who received an average of 70% of the call cost.
"Unthinkingly I just put the brochure on the fax machine. It went through at a very, very slow speed," he said.
He contacted the Independent Committee for the Supervision of Standards of Telephone Information Services (ICSTIS), which has carried out a series of investigations after receiving hundreds of complaints from hoteliers across the UK.
Premium rate
This has already led to action against several companies.
ICSTIS spokesman Rob Dwight said the firms were trying to disguise the 090 premium rate number as an ordinary telephone number.
He said: "The message we are trying to get across to hoteliers is all premium rate numbers begin 090, so if somebody gives that number it will be premium rate."
But he stressed that the culprits made up a very small proportion of the 20,000 or so companies using 090 numbers.
And he added: "I wouldn't go so far as to call it fraud, but it's definitely a case of breaching the rules and misleading hoteliers."
'Reman vigilant'
Attempts had also been made to involve estate agents in the scam, he added.
Mr Dwight warned all hotel staff to remain vigilant and urged them to contact ICSTIS if a caller did not provide prices, identity or contact details.
He added: "If you get a call that you are a wee bit doubtful about, check that it's not a premium rate number - and, if it is, don't fax anything."