BBC.The UK Competition Commission has ruled against the merger of Ticketmaster and concert promoter Live Nation.
In a provisional ruling, it said it was concerned about the joining of the world's largest ticketing firm and the world's biggest concert promoter.
Such a deal would limit the development of competition in the market for sales of tickets to live music, it said.
The US Justice Department is also investigating the proposed merger - which was announced in February.
The two companies have said the merger would improve ticket price options, increase attendance at events and make ticket technology better.
Live Nation not only operates the majority of concert venues, but also manages many of the artists who play in them.
The company has signed artists including Jay-Z and Madonna to deals that include touring, publishing and albums, as well as huge concert promotion deals with the likes of U2 and Shakira.
Ticketmaster are already a complete scam, their booking fees and other nonsense are crazy. If this was allowed to go ahead the new company would have complete control over just about every major gig/artist, awful.