Travel firm Thomson may be breaking law, Which? says
The consumers' association Which? says the UK's largest travel firm could be breaking the law because of the way it promotes some deals.
The BBC has found that Thomson, owned by TUI Travel, ran an advert suggesting only a few seats were left on a flight.
It then released more seats that were offered at a much lower price.
The Association of British Travel Agents (ABTA) said there could be more clarity in the way some offers were advertised.
Mike O'Keeffe, who runs a dry cleaning business in Bristol, contacted the BBC after he felt he had been misled when purchasing seats for family members on a Thomson flight to Florida.
He booked two seats in early August to fly later this month, paying £496 per person after seeing the words "hurry only 3 seats left" next to the price.
But the next day he found that more seats had become available.
They are currently selling for £411 on the same plane to the same destination.
''When my sister-in-law said she'd like to come too, I checked to see if the last seat was still there and it was," Mr O'Keeffe said.
"I then checked to see exactly how many seats were left and I could book up to eight.
"I felt very aggrieved, because I was pressured into buying those seats when in fact more were available, and they are now being sold for a lower price,'' Mr O'Keeffe added.
TUI Travel, which owns Thomson, told the BBC that the majority of its holidays were sold on seven and 14 night durations.
''When the initial booking was made we had very limited availability on the specific duration chosen," the travel firm said.
"After the booking was made, our seat availability was reviewed and it became apparent that whilst we had no availability on shorter durations, we did however have greater availability on longer durations and were in a position to be able to amend the durations against some seats.
"The process of converting longer durations to shorter durations and vice versa when availability is low or sold out is common practice within the industry and something that as an operator we do occasionally throughout the season,'' TUI explained.
The consumers' association Which? says it believes the firm is breaking the law.
''It's actually illegal under the consumer protection regulations any time someone is forcing you to making a decision," said Rochelle Turner, head of research for Which? Holiday.
"For example if you see something that says only three seats available, you've been pressured into making an immediate decision and that's actually based on false information in this case,'' she explained.
ABTA said that charter companies do often allocate seats in a different way to firms operating scheduled flights.
But it said improvements in the way they were promoted could be made in some cases.
''Certainly for ABTA and our members it's important that when something is on offer it's clear on what basis it is being offered," said Sean Tipton, spokesman from ABTA.
"So perhaps on that area some companies should think twice about how they word their offers.
''But fundamentally if you are talking about price differentials, it's just as possible that these seats that were allocated from a different class, could go up in price instead of down," he explained.