Ticket resale website Viagogo has announced it will buy rival StubHub in a deal worth 4 billion US dollars (£3.1 billion).
Viagogo said the takeover would create more choice for customers, but critics warned the company has a “long history of ripping off” music and sports fans.
Eric Baker, Viagogo’s founder and chief executive, also co-founded StubHub but left before the business was sold to eBay for 310 million US dollars (£240 million).
“Bringing these two companies together creates a win-win for fans – more choice and better pricing,” he said.
Adam French, Which? consumer rights expert, said: “Viagogo has a long history of ripping off music and sports fans and had to be threatened with court action after failing to provide vital information to customers, so any move to increase its grip on the secondary ticketing sector is likely to be a worry for consumers.
“The regulator should closely examine this deal and the impact it could have on competition in the sector to ensure consumers do not lose out.”
In July, Viagogo was suspended as an advertiser by Google after the search engine giant found the firm had breached its policies.
In March, MPs warned the public against using Viagogo over concerns it did not comply with consumer laws.
A report from the Digital, Culture, Media and Sport (DCMS) Committee said the firm had “caused distress for too many music fans for too long”.
Competition watching the Competition and Markets Authority said it was going ahead with legal proceedings against the company after repeated warnings over its compliance with consumer protection law.
It suspended the court action in September, saying Viagogo had addressed its concerns.