The British Phonographic Industry (BPI) has asked UK internet service providers (ISPs) to unblock music promotion site The Promo Bay.
Last week, BPI had sent a letter to the Pirate Party UK chief Loz Kaye requesting to close their Pirate Bay proxy service.
The BPI told the Open Rights Group (ORG) that it had written to ISPs to unblock the site.
Open Rights Group executive director Jim Killock said: "The BPI intend to obtain blocking orders for some 50-100 websites. Each order allows the BPI to create a ban list of clone sites or IP addresses."
"These ban lists could end up blocking perhaps 500 or more domains and IP addresses, all the at the behest of the BPI," Killock said.
"There is a clear need for transparency, as mistakes are already being made, and are only being corrected because of public pressure. We call on ISPs and the BPI to publish the blocking lists in the name of legal transparency and public accountability."
Recently, ORG wrote to Virgin, BT, O2, TalkTalk and Sky to ask them why the PromoBay.org is being blocked.
In response to ORG's letter, Virgin confirmed that the site was supplied to them as a domain to be blocked.
Earlier this year, UK high court ordered several country's ISPs to block access to the file sharing site, Pirate Bay.