In a letter to the Financial Times, the group, which also includes UK ISPs such as BT and TalkTalk, said the amendment to the Digital Economy Bill has "obvious shortcomings" and will lead to an "increase in internet service providers blocking websites accused of illegally hosting copyrighted material without cases even reaching a judge".
The amendment to Clause 17 of the bill, which was passed by the House of Lords last week, gives High Court judges the power to force ISPs to block access to any website with a "substantial" amount of copyright infringing content, such as YouTube.
"Endorsing a policy that would encourage the blocking of websites by UK broadband providers or other internet companies is a very serious step for the UK to take", the companies said.
"There are myriad legal, technical and practical issues to reconcile before this can be considered a proportionate and necessary public policy option. In some cases, these may never be reconciled. These issues have not even been considered in this case."
The companies claim the amendment has been rushed through without consultation with industry or consumers.
The letter comes at BT chief executive Ian Livingstone suggested web users accused of illegally downloading should be fined rather than face a temporary suspension from the web.
The Digital Economy Bill also sets out a 'three strikes' rule that will see web users accused of illegally file-sharing issued with warning emails and letters.
Repeat offenders will face technical measures, which the government said would be in the form of "a bandwidth restriction, a daily downloading limit or, as a last resort, temporary account suspension".
Livingstone told the BBC the proposals go against natural justice, and instead they should be fined, which they could choose to pay or fight in court.
He said this method would "create a fund", although he didn't specify what the cash would be used for, an would create "some good, rather than getting some hurt out of people infringing copyright".