America is fond of chiding other nations about freedom of speech in the internet age. Leaders including President Obama and Secretary of State Hillary Clinton are constantly reminding their global counterparts, especially in places like China, that internet censorship is a detriment to open government and honest self-rule. Yet, the Obama administration has used tactics that smell of censorship, and Congress is making common cause with a corporate cartel that wants to turn the internet into little more than an enhanced form of cable television. In the name of protecting copyright holders, they would censor the internet and force entrepreneurs to get permission to innovate.

Hollywood and the music industry lead the copyright cartel. They have been at war with the internet – and all technology they can't control – since they realised that digital technology was creating huge challenges to their way of doing business. They have allies, to varying degrees, in other industries that include book publishing, software and pharmaceuticals, all of which are seeing their markets change and, in some cases, erode.

They'd already persuaded the US Congress to enact copyright laws that are grossly unbalanced on the side of the copyright holders and against the rights of users. Now, they're back at the trough, and this time, they want to eliminate one of the few provisions that has any balance whatever: the so-called "safe harbor" giving immunity to websites that host other people's postings. (The people doing the posting have no immunity.) When notified of a violation, sites must take down that material until and unless the original poster challenges that takedown.

Without safe harbor and several related provisions, much of the internet as we know it could not exist, because forcing websites to pre-screen everything that comes from users is untenable. And that is one reason why the copyright cartel's friends and puppets in Congress have introduced the Stop Online Piracy Act (Sopa), a bill designed, among other things, as an end run around safe harbor.

Today, the House Judiciary Committee is holding a hearing on Sopa (pdf). It's a sham, of course: a stacked-deck collection of proponents with little time granted to people who want to keep the internet open and free for innovation. But Sopa and a companion bill in the Senate are being fast-tracked by politicians who either don't realise what they are doing or don't care about the damage they would cause to speech and innovation.

What Sopa's proponents say is simple: online infringement is so bad and so prevalent that extraordinary measures are now needed to slow it down. They say they only want to go after the most egregious violators of copyright. A movie industry association blogger wrote that it would "target foreign rogue sites that knowingly and deliberately engage in the illegal distribution of stolen content, including movies and television shows, for profit".

This is a partial truth, concealing a huge lie. The legislation is vaguely written and over-broad – no doubt, deliberately – and it would give copyright holders weapons that would go far, far beyond the "foreign rogue sites" the industry claims are the target. The Electronic Frontier Foundation has ably explained much of the damage this bill could cause, but here are a few especially bad provisions.

For example, copyright holders could invite payment systems such as PayPal, Visa and Mastercard to cut off services to allegedly infringing operations – and the payment systems would be granted immunity from lawsuits, giving them an incentive to do Hollywood's bidding with little recourse for the affected sites.

The bill would also enshrine the already dubious practice of ordering internet domain-name service providers (DNS) to essentially blacklist web addresses. So if you typed "atargetedsitename.com" into your browser, you would not be taken there, even if the site existed. This breaks a fundamental feature of the internet, and is slated to get worse.

It also could force software developers to put censorship tools into their products or face lawsuits or worse. Current copyright law – remember, it's already balanced on the holders' side – has been used to chill activities of people, including software developers and researchers, who were, by no stretch, engaged in infringement.

The damage Sopa would cause to existing services is bad enough. But the longer-range damage is literally incalculable, because the legislation is aimed at preventing innovation – and speech – that the cartel can't control. If this law had been passed years ago, YouTube could not exist today in anything remotely like the form it has taken. The cost of serving Hollywood's interest would have been too high, but the reality is that investors would have never gone near the project. They would have been persuaded that the risks were too high.

In recent days, the technology industry has become more outspoken about the danger (pdf), and public interest organisations are shouting their alarm (pdf). But the opposition has been late to recognise the threat, and is outmatched by the lobbying clout of Hollywood and the cartel overall.

Meanwhile, the major media have been essentially silent on the issue. I'm not surprised. Big Media is an ally and member of the copyright cartel – and there may be more than a few people in traditional news organisations who fear the internet more than they worry about stifling speech.

The anger over this legislation is mounting, thanks to grassroots opposition. Congressman Ron Paul, currently a Republican presidential candidate, is one of a growing number of representatives to oppose it. It may not be too late to stop the Great American Firewall.

Today, Wednesday, has been proclaimed "Web Censorship Day" by a coalition of people and organisations involved in this fight. They're putting banners and popups on websites to demonstrate the danger of Sopa. Listen to what they are saying; this is your internet, not Hollywood's, but it is in clear danger.