The UK's major internet service providers have been asked to block three more file-sharing websites, the BBC can reveal.
The British Phonographic Industry (BPI), which acts on behalf of rights holders, wants ISPs to prevent access to Fenopy, H33t and Kickass Torrents.
The BPI alleges that the sites are illegally distributing music.
The ISPs told the BBC they would comply with the new demand, but only if a court order is put in place.
It follows a separate court order in April which saw popular file-sharing site The Pirate Bay blocked in the UK.
The biggest ISP, BT, said it was also "currently considering" its options.
The letter, which was not intended to go public, was sent to six ISPs last week, namely BT, Sky, Virgin Media, O2, EE and TalkTalk.
It is understood that the BPI is hoping all three sites will be blocked before Christmas - far more quickly than the process has taken previously.
According to web monitoring firm Nielsen, over a million unique users from the UK visited the three websites in September.
Pirate Bay precedent
In April, the BPI was successful in getting a high court judge to order the same six ISPs to block The Pirate Bay, which was regarded as one of the most visited file-sharing websites on the web.
"Like The Pirate Bay, these websites are profiting illegally from distributing music that isn't theirs, without permission and without paying a penny to the musicians, writers and producers who created it," a spokesman for the BPI told the BBC.
"It is plain wrong. The existence of these sites damages the growth of Britain's burgeoning digital music sector."
Over the following months, all of the ISPs complied with the ruling, blocking access to the site for their customers.
With this latest request, the BPI is looking to avoid such a lengthy process. However, none of the ISPs said they were prepared to block the sites voluntarily, and would only do so if forced by the courts.
Adam Rendle, a copyright specialist with London-based law firm TaylorWessing, said it is possible that the process to block Fenopy, H33t and Kickass Torrents could be quicker than in previous cases thanks to precedents set previously.
"Whether the BPI can do that in time for Christmas is a question of the court's availability," he said.
"Two months to issue the proceedings and get a decision? It's ambitious but it's not impossible - if the court can be convinced that it should be dealt with that quickly."
Loss of traffic
Jim Killock, a campaigner with the Open Rights Group, argued that consumers' interests were not being properly represented.
"Web blocking is an extreme response," he told the BBC.
"If courts are being asked to block websites they need to be taking into consideration the rights of users and any legitimate usage of those sites.
"It isn't clear whether a conversation between a judge, ISPs and rights holders is going to sufficiently represent the needs of users."
Critics of website blocking say it is ineffective.
Days after the Pirate Bay blocking, various other services were set up allowing users to access the site through alternative means.
One ISP, which did not want to be named, revealed that despite an initial dip, illegal download traffic on its network recovered quickly within just a week of the Pirate Bay block.
However, the BPI defended the action, saying that the block had a significant effect on the amount of traffic visiting the Pirate Bay site.
This claim is backed up by Nielsen, who told the BBC that since the April court order, The Pirate Bay has lost three quarters of its visitors.