Hamilton fans in the UK that bought tickets to the hip-hop musical on resale websites for up to £6,000 ($8,033/€6,807) could face being turned away from London’s West End Victoria Palace theatre.

The warning comes on the heels of the Competition and Markets Authority’s (CMA) move to take enforcement action against resale sites suspected of breaking consumer protection laws.

Despite their best efforts, including the fact that production company Delfont Mackintosh banned resale tickets for the show, Viagogo was spotted advertising dozens of tickets with huge mark-ups.

Tickets for the Broadway spectacle completely sold out after going on sale in January. £10 tickets can still be obtained through a daily lottery up until the day of each showing.

Ticketmaster, which is the official seller for Hamilton, warns buyers: “Reselling of any Hamilton ticket is strictly forbidden,” adding that anyone found to have bought seats through a secondary ticketing site will be “refused admission.”

Viagogo, in a statement on its website, says: “These types of entry restrictions are highly unfair and in our view, unenforceable and illegal.”

A ticket listed on Viagogo for the last show before Christmas was advertised for £4,400, which rose to £5,905 when VAT was included and had an additional £1,500 booking fee.

The CMA raided Viagogo and rival StubHub’s offices during its investigation, warning last month it had “gathered evidence which it considers reveal breaches of the law” by ticket sites.