Three holiday package providers have been warned they face fines for changing their prices while customers are booking.

The Netherlands Authority for Consumers and Markets (ACM) imposed conditional penalties on the three unnamed companies, meaning they will be fined if they break the rules again.

The ACM said consumers must be sure that the price they see when they browse the website is the price they actually pay with no hidden costs, so they can search for the best deal.

“For consumers, the price is one of the most important criteria for choice,” said ACM board member Cateau Hijmans van den Bergh. “People should be able to easily compare prices from the different providers.

“This is only possible if the first price shown is the price for which the trip can actually be booked, including all mandatory costs. That’s why we warn consumers who want to book a holiday trip ‘last minute’.”

But consumers aren’t the only ones being warned. Two years ago, ACM looked into the pricing practices of 12 package travel providers and found 11 of them incorrectly listed mandatory additional costs, such as tourist tax.

All 12 companies now accurately list their prices, but when it comes to booking trips for the price first shown, three companies are still not in compliance.

“If the trip cannot be booked for this price, there is deception,” says the AMC, which says travellers should be able to easily compare prices from various providers.

It cited the example of a trip to Bali that was offered for three people for 2,400 euros. But when people went to book the trip, the price increased to 3,000 euros – a 25% increase.

The AMC said people are less likely to switch to another offer or other provider when in the middle of booking a specific trip, meaning they will lose the money they could have saved by accepting a different offer.

“This is bad for consumers and a form of unfair competition,” said the AMC. “The price of the trip must be stated including all mandatory costs. All other costs must also be visible at a glance.”