MPs go to the Commons today for the second reading of the controversial Digital Economy Bill.
Among other things, the bill will allow websites to be blocked and internet users to be cut off for alleged online copyright infringements.
The government has already said it will introduce a radically rewritten clause to cover the processes by which it hopes to fight online piracy and protect intellectual property. The provisions could cost internet service providers up to £15m to implement.
Advertisements in the Times and Guardian newspapers today call for MPs to have a thorough debate of the bill rather than pass it in the "wash-up" horse-trading between front benches as this parliament nears its end.
The advertisements were paid for with money collected by public subscription by two civil rights campaigners, Open Rights Group and 38Degrees, and supported by a letter writing campaign that resulted in more than 20,000 letters to MPs.
Open Rights Group executive director Jim Killock said, "People use the internet for work, education and free speech. You cannot take that away without a very serious reason. Copyright infringement allegations are not on that scale."
He said the threshold at which someone would be considered a music or video pirate worth acting against had still to be negotiated. Some thought it would be 50 illegal downloads.
Killock said songs cost as little as 35p on some legal download websites. This meant the alleged commercial harm suffered by the rightsholder was just £17.50. A Finnish study showed that alleged music pirates also buy the most music and were 10 times more likely to buy music legally.
Over the weekend the BBC revealed a letter acquired under a Freedom of Information Act request that shows Hollywood lobbying business secretary Peter Mandelson to increase pressure on internet service providers to block alleged pirates.
While on holiday in Corfu last year Mandelson also met US music producer David Geffen, just before asking for more Draconian measures against alleged online pirates to be added to the bill. Mandelson later denied the meeting had anything to do with the bill.
The Commons debate is scheduled to start at 3.30pm, and may run until 10pm.