The UK competition watchdog has launched investigations into the Trainline, Virgin Atlantic and Red Driving School over concerns customers were not shown full prices upfront.
Consumers affected could get compensation if it is found that the companies broke the law, the Competition and Markets Authority (CMA) said.
The probes are part of a wider clampdown by the regulator over misleading pricing practices.
It said this includes practices were mandatory charges are separated from the headline price or added later in the buying process, known as drip pricing.
Shoppers could therefore face unexpected costs or have to calculate the total cost of a purchase themselves.
“Such practices can also impact competition between businesses, as a firm using drip pricing may falsely appear to be cheaper than a competitor and attract more customers,” the CMA added.
Emma Cochrane, executive director for consumer protection at the CMA, said: “Clear pricing helps people compare offers confidently and choose the option that works best for them.
“Unexpected mandatory charges make this much harder, which is why the CMA initially put these firms on notice over concerns about their pricing practices and is now opening formal investigations.”
A Trainline spokesman said: “Trainline is committed to offering customers a transparent booking experience with clear pricing and genuine value.
“We’ve proactively engaged with the CMA over several months and we are taking proactive steps to enhance how certain fees are presented to our customers.
“We will continue engaging with the CMA to address their questions.”
Virgin Atlantic and Red Driving School have also been contacted for comment.
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