The UK's music industry body is demanding that a service offering a workaround to access banned site The Pirate Bay is shut down by its owner.
Pirate Party UK, a political group, has set up a proxy that can be used to reach the piracy site even though it has been blocked by the UK courts.
The British Phonographic Industry (BPI) has written to the party's leader Loz Kaye to request the proxy's removal.
Mr Kaye told the BBC his party was "seeking legal advice".
"We've been clear all along, the reasons for the proxy," Mr Kaye added.
"It is a legitimate tool, for a legitimate political end."
Pirate Party UK - which is not affiliated with The Pirate Bay - said it created the proxy website as an act of "freedom of expression" and to support "the right to share information and ideas without interference and that censorship is never the right answer".
However, in a letter seen by the BBC, BPI chief executive Geoff Taylor told Mr Kaye: "Freedom of expression is not an absolute right.
"It comes with a duty to respect the rights of others, including those whose talent, hard work and investment help to create music and other entertainment."
Since launching the proxy, the Pirate Party UK's website has rocketed in popularity.
According to web metrics firm Alexa, the party's site was ranked 1,943 in the UK prior to the Pirate Bay ban.
The site is now ranked 147 - higher than the likes of Netflix, the Huffington Post and the NHS. Mr Kaye has previously boasted that it sent more than two million hits to the Pirate Bay every day.
Mr Taylor argued that the Pirate Party UK's arguments to support the proxy were a "complete red herring".
"We are passionate believers in freedom of speech," Mr Taylor said.
"But it doesn't justify The Pirate Bay helping themselves to other people's work.
"The human rights implications of blocking this illegal site have been fully considered by the High Court.
"Whatever their views, Pirate Party UK are no more above the law than anyone else."
Mr Taylor has requested that the Pirate Party UK respond to the BPI's letter by 6 December.
Mr Kaye told the BBC he intended to honour that request.