An influential group of MPs and peers has said the government's approach to illegal file-sharing could breach the rights of internet users.
The Joint Select Committee on Human Rights said the government's Digital Economy Bill needed clarification.
It said that technical measures - which include cutting off persistent pirates - were not "sufficiently specified".
In addition, it said that it was concerned that the Bill could create "over-broad powers".
"The internet is constantly creating new challenges for policy-makers but that cannot justify ill-defined or sweeping legislative responses, especially when there is the possibility of restricting freedom of expression or the privacy of individual users," said Andrew Dismore MP and chair of the Committee.
A spokesperson for the Department for Business, Innovation and Skills (BIS), which oversees the Digital Economy Bill, said that government had "always been clear that [its] proposals to deal with unlawful file-sharing should not contravene human rights".
The Select Committee only examined the parts of the Bill that focus on plans to tackle illegal file-sharing as well as a controversial amendment to copyright law.
"The concern we have with this Bill is that it lacks detail," said Mr Dismore. "It has been difficult, even in the narrow area we have focussed on, to get a clear picture of the scope and impact of the provisions."
The Digital Economy Bill was outlined in the Queen's speech in November 2009.
One of the most hotly-debated elements is the so-called "three strikes rule" that would give regulator Ofcom new powers to disconnect or slow down the connections of persistent net pirates.
The Committee said it had concerns about "technical measures" like these and how they would be applied.
For example, the government has not specified whether a whole household could be cut off if only one member of a family was identified as a persistent file-sharer.
The committee said that measures such as this have "the potential to breach internet users' rights" and had not been "sufficiently specified to allow for an assessment of proportionality".
Jim Killock of the Open Rights Group, which has campaigned against the measures, said that disconnecting alleged file-sharers was "draconian and unpredictably damaging".
A spokesperson for BIS said: "slowing down or suspending peoples broadband would only be invoked following several clear warnings".
Any technical measures would require "secondary legislation", he added.
"There will be no technical measures imposed at all if the initial measures taken are as successful as we expect."
The Committee also examined Clause 17 of the bill, which would give the government the power to amend the copyright law without passing further primary legislation.
The clause has proved controversial. In late 2009, a consortium of web companies including Facebook, Google, Yahoo and eBay wrote to the business secretary Peter Mandelson objecting to the clause.
The web firms urged MPs to remove the clause, which they said could give government "unprecedented and sweeping powers" to amend copyright laws.
The Select Committee said that it had been told that changes would be made to the clause to ensure that any amendments to copyright law would be "better scrutinised by Parliament".
"Despite this the Committee remains concerned that Clause 17 remains overly broad and that parliamentary scrutiny may remain inadequate," it said.
The BIS spokesperson said that government had already tabled "a series of amendments which aim to clarify the breadth and scope of clause 17".
The Digital Economy bill is currently being scrutinised by the House of Lords.
It was dealt a blow recently when Sion Simon, one of the MPs charged with pushing it through parliament, announced he was standing down.