Rail passengers seeking compensation for delayed journeys are required to submit up to 24 pieces of information to make a claim.
Consumer group Which? is calling for the system to be simplified after it found companies were asking for between 10 and 24 separate details.
Greater Anglia, London Northwestern, ScotRail, Transport for Wales, and West Midlands Trains asked for the most.
Rail bosses said the requirements guarded against fraudulent claims.
The amount of compensation which can be claimed following disruption varies between train companies and depends on the length of delay and the type of ticket.
Recent research from independent transport watchdog Transport Focus found that just 35% of passengers who are eligible for compensation submit a claim.
Which?, which has previously filed a super-complaint about the delay compensation system, argued that the system was “fragmented and confusing”.
“This leads to people losing out on a lot of money when they have already suffered enough from unacceptable levels of delays and cancellations,” said Alex Hayman, from Which?.
The consumer group found that some of the most complex claims forms requested 13 different pieces of information about the ticket. These included how the ticket was paid for and whether it was at peak time.
Yet, it argued that most of this information was clearly displayed on a photo of the paper ticket – which all but one company required to be uploaded as proof of purchase.
Anthony Smith, chief executive of Transport Focus, said: “It is now important that train operators actively encourage passengers to claim, making it quick, easy and automated as soon as possible.
“[We] will be campaigning to ensure more passengers affected by delays or cancellations claim. There is no better way for passengers to ensure the rail industry listens to them.”
Jacqueline Starr, chief operating officer from the Rail Delivery Group, which represents the rail industry, said that the questions were asked to ensure passengers “receive what they are entitled to as quickly as possible while also guarding against fraudulent claims”.
“We are doing more to encourage claims, including sending reminders to people who booked online, making announcements on trains and handing out claim forms, which has led to an 80% increase in compensation over the last two years to £81m a year,” she said.
The government said it wanted to see a “one click” system of online financial redress for passengers by the end of current franchises, some of which are completed in 2025.
Which?’s research found that Chiltern Railways and Heathrow Express asked for the fewest details, requiring 10 pieces of information. Several rail companies offer automatic compensation to customers with certain tickets.