Banning web users suspected of illegally downloading content from the internet could breach human rights legislation, says the Joint Select Committee on Human Rights.
According to the group of MPs and members of the House of Lords, the proposals set out in the Digital Economy Bill reference 'technical measures' which could be employed to block internet pirates' web connections.
However the committee said the technical measures had not been "sufficiently specified".
"The concern we have with this Bill is that it lacks detail," said Andrew Dismore MP and chair of the Committee.
"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."
Dismore added that the internet is constantly creating new challenges for policy makers but "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".
The Department for Business, Innovation and Skills (BIS), which is responsible the Digital Economy Bill, said the proposals do not contravene human rights.
"Slowing down or suspending people's broadband would only be invoked following several clear warnings," said a spokesman, adding that the technical measures will require "secondary legislation".
ISP TalkTalk has also voiced its concerns over the 'three strikes' rule.
In October last year, Andrew Heaney, the executive director of strategy and regulation at TalkTalk, told The Guardian: "If the government moves to stage two we would consider that extra-judicial technical measures and would look to appeal the decision [to the courts] because it infringes human rights".
As a result of its concerns, the ISP launched the Don't Disconnect Us campaign which aims to ensure the government gives every web user accused for illegally file-sharing a fair trial before cutting them off from the web.