UK based internet service provider Tiscali has denied speculation that it has blocked some of its users from playing online games.
A number of Tiscali customers have complained of slow connection speeds and an inability to connect to popular gaming servers.
There are now around 650 messages discussing the problem on the company's broadband service support pages.
Customers' claims have gained backing from a community manager for the online game Call of Duty 4, who believes the company may have blocked peer-to-peer access for some users, meaning that they cannot access the bandwidth-heavy gaming servers.
A Tiscali spokesperson told gaming website Next-Gen: "Reports suggesting that we were deliberately blocking specific games are incorrect. We are constantly working to upgrade and refine our network to ensure our customers can enjoy their favourite applications."
The spokesperson added that work is being undertaken to ensure the problem is resolved.
Tiscali also came under fire last week as a number of customers bought from Pipex complained of loss service in the switchover.