BT and TalkTalk go to the High Court in March to challenge legislation aimed at tackling illegal filesharing and protecting intellectual property rights online.
The companies, two of the UK's largest broadband providers, argue the Digital Economy Act is seriously flawed and conflicts with European law.
They warn it could infringe internet users' "basic rights and freedoms" and was given "insufficient scrutiny" in Parliament when it was rushed through in the dying days of the last Labour government.
The Coalition says it has no plans to repeal the Act.
A spokesman at the Department for Business, Innovation and Skills (BIS)
said today: "The Government believes the Digital Economy Act is consistent with EU legislation and contains sufficient safeguards to protect the rights of consumers and Internet Service Providers."
The Act "sets out to protect our creative economy from the threat of
online copyright infringement, which industry estimates costs them 400m a year".
BT and TalkTalk's application for judicial review is listed to be heard at a three-day hearing at the High Court in London beginning on March 22.
They argue the way the new law was introduced was procedurally flawed and could potentially lead to millions of innocent customers having their privacy invaded.
A number of MPs and pressure groups voiced concern following the controversial Digital Economy Bill being given royal assent after just two hours of debate in the Commons.
The parliamentary inquiry into the protection of intellectual property (IP) rights online was recently suspended pending the High Court challenge.
The IP framework brought in by the new Act was set to be assessed by the culture, media and sports committee.
The submission deadline for written evidence has been extended, and no public evidence sessions will be held until the BT/TalkTalk judicial review has concluded.