Consumer group Which? has launched the second part of a campaign to get online ticketing companies to justify added costs to customers when buying tickets.
It says it has more than 37,000 people pledging their support for its Play Fair on Ticket Fees campaign.
Which? says it has named and shamed online ticket companies who it says are breaking advertising rules by not being clear about extra booking costs.
The organisation says companies need to explain what those costs are for.
Alex Neill is head of campaigns for the organisation and says they have managed to get seven ticketing companies to agree to show their costs up front, such as delivery costs.
"Our campaign is about getting the big ticket companies to not hide their fees, to show them up front, and then to justify how expensive these fees are and what they are actually for.
"Why are they so different? They can vary from nothing to up to more than a third, which is a huge variation. So we want to know what that's for."
However, other ticketing companies are not breaking the law by adding extra administration charges to tickets, such as charges for paper printing at home.
But Alex Neill says concert-goers are telling them that they're fed up with paying more.
"It's something that people have told us they're really fed up about," he said. "That's what we're saying to the companies, you need to explain what these fees are for.
"There's nothing in the rules, but that's what we're campaigning for, this isn't fair and people are fed up with it."
The first part of the Which? campaign took place in October and November, when researchers found varying prices for the same events on different ticketing websites.
The research uncovered that a £25 ticket to see comic Jimmy Carr incurred extra fees of £9.50.
Jenny Willott, minister for employment relations and consumer affairs in the department for business, innovation and skills and women, says ticketing companies need to more open about their fees.
"Hidden charges when buying tickets online need to come to an end," she said.
"Not only are they unfair for the customer, but they also damage the reputation of businesses.
"The sector has made some progress on this with more transparency about what the final price will be and I welcome Which? efforts to help highlight this issue.
"We want to make sure people can compare prices across the board so they can see if they're getting a bad deal and if so choose to take their business elsewhere."
In a statement Ticketmaster said: "Ticketmaster is driven by what real fans want; a safe, convenient way to purchase tickets to the events they love.
"Our investment in our people, UK call centres and state of the art technology make that all possible.
"Ticketmaster constantly reviews its fees and processes to ensure that they adhere to the current legislation, employ the latest technology, respond to changes in the market and meet our clients' and customers' preferences.
"However, for Which? to suggest that we have made changes as a result of their report is at best misleading and as a matter of fact not true."
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