BT has been ordered to block access to file-sharing website Newzbin2 within two weeks.
A High Court judge enforced a ruling by the judge in July that BT must block its customers from accessing Newzbin2 in response to a case brought by six US film studios.
BT is the UK's biggest internet service provider (ISP) with nearly six million customers. This is the first time a British ISP has been ordered to prevent its customers from visiting a website to protect rights holders' revenues.
The ruling ended in the judge deciding that BT was aware the site was being used for copyright infringement "on a large scale", according to the Guardian.
Justice Arnold asked BT to bear the costs of implementing the order as well.
"In my judgment, the costs of implementing the order should be borne by BT," Arnold said.
"BT is a commercial enterprise which makes a profit from the provision of the services which the operators and users of Newzbin2 use to infringe the studios' copyright. As such, the costs of implementing the order can be regarded as a cost of carrying on that business."
He also agreed with the lawsuit that BT should block "any other IP address or URL whose sole or predominant purpose is to enable or facilitate access to the Newzbin website".
"Furthermore, I do not consider that the studios should be obliged to return to court for an order in respect of every single IP address or URL that the operators of Newzbin2 may use," Arnold added.