TalkTalk and BT have filed legal papers at the High Court seeking a judicial review of the Digital Economy Act.
The companies hope to have the legislation repealed before it comes into force after what they claim was insufficient scrutiny when it was rushed through parliament in the pre-general election wash-ups.
Andrew Heaney, executive director of TalkTalk, told V3.co.uk that the action is necessary to provide "legal clarity and avoid a situation where we spend tens of millions only for the Act to be later overturned".
Heaney added that TalkTalk is not sure whether any other ISPs or groups will join the action, but claimed that "many share our view".
Gavin Patterson, chief executive of BT Retail, also cited a lack of clarity in the Digital Economy Act, and questioned whether the proposed legislation is legally sound.
"It is disappointing that we feel the need to take action but we have no choice. We have to do this for our customers who otherwise run the risk of being treated unfairly," he said.
"Our dispute is not with the current government but with the previous administration which pushed this through without due process. We need clarity about whether this legislation is compatible with important EU laws."
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