BT and TalkTalk may go to court to try and overturn the Digital Economy Act - passed just before Parliament was dissolved for the election.
Two of the largest ISPs in the UK want the High Court to confirm that the Act is legal and that disconnecting persistent file sharers does not infringe basic rights.
Apart from the legality of the proposals the two companies are also concerned about how it will be implemented.
As we exclusively revealed here Ofcom is considering leaving smaller ISPs and mobile ISPs out of the reach of the law. The argument is that such small companies would find tracking pirates more difficult or more of a financial strain.
But Andrew Heaney, executive director of TalkTalk, told the BBC: "It means we could have huge swathes of customers moving to smaller ISPs to avoid detection."
There are also concerns that the Act as it stands could conflict with European law, which protects ISPs from responsibility for the content they carry. Privacy rights might also be curtailed by the need for ISPs to effectively monitor what their customers are doing.
Heaney also complained that the music industry had done little to help itself and had taken no court action itself against pirates. He said: "It is outrageous that they are coming begging at our door but are not helping themselves." ®
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