A couple say they have been "fined" £100 by a Blackpool hotel for leaving critical comments on travel review website Trip Advisor.
Tony and Jan Jenkinson posted the negative comment after being unimpressed with the one night they spent at the Broadway Hotel.
The couple, from Whitehaven, later found £100 charged to their credit card. The hotel said its policy was to charge for "bad" reviews.
Trading Standards are investigating.
Officials believe the hotel may have breached unfair trading practice regulations.
The manager of the hotel, on Burlington Road West, was unavailable when contacted by the BBC.
'Freedom of speech?'
The hotel policy, contained in a booking document, reads: "Despite the fact that repeat customers and couples love our hotel, your friends and family may not.
"For every bad review left on any website, the group organiser will be charged a maximum £100 per review."
Mr and Mrs Jenkinson were on their way to visit family in Oxford when they decided to split up their journey.
They said they only chose the hotel because it had a car park and paid £36 for the double room.
Retired van driver Mr Jenkinson, 63, said the details of the charge were in the booking documents, but his wife did not have her glasses on and signed it without reading the small print.
Mr Jenkinson said he intended to fight the charge, adding: "Annoyed isn't strong enough for how I feel about this, what happened to freedom of speech?
"Everybody we have spoken to says they (the hotel) are not allowed to do this."
John Greenbank, north trading standards area manager, said it was a "novel" way to prevent bad reviews.
'Get service right'
He said: "I have worked for trading standards for many years and have never seen anything like this.
"The hotel management clearly thinks they have come up with a novel way to prevent bad reviews, however we believe this could be deemed an unfair trading practice."
The couple have sought a refund via their credit card company.
Councillor John McCreesh, cabinet member for trading standards, said: "Customers need to be free to be honest about the service they're getting.
"Other customers depend upon it. Hotel owners should focus on getting their service right rather than shutting down aggrieved customers with threats and fines.
"People should have the right to vent their disappointment if a hotel stay did not meet their expectations and should not be prevented from having their say."