YouTube's logo is seen against the flag of the European Union. Omar Marques | SOPA Images | LightRocket | Getty Images

European parliamentarians are set to vote on a controversial copyright law that some critics believe could stop people from sharing memes and articles online. Lawmakers in Strasbourg, France, will cast their votes on the European Union's new copyright directive on Wednesday. The result of that vote could determine whether large tech companies including Facebook, Twitter and Google are forced to use filtering systems that block copyrighted content. Such firms may also be required to pay news organizations for the rights to share articles and other copyright-protected content like scientific papers, something that critics have dubbed a "link tax." The proposed law has ignited a fierce debate, luring high-profile figures from both the tech and media industries. On the tech side, voices arguing against the legislation include internet pioneer Tim Berners-Lee and Wikipedia founder Jimmy Wales. Big names within the media sector, who are mostly for the reforms, range from former Beatle Paul McCartney to French DJ David Guetta. The European Parliament had initially voted to delay the proposed law in July, rejecting a closed-door debate that would have sped up the process of passing it into law.

Why is it so controversial?

Two particular parts of the directive have attracted the most criticism from pro-internet freedom activists. One is Article 13. This section calls on internet giants to take "appropriate and proportionate" measures to prevent user-generated content that infringes a rightsholder's copyright. This part of the law has come under heavy criticism over concerns that tech giants could end up using automated content filtering systems. The law states that "effective content recognition systems" should be put in place by digital companies to prevent copyrighted materials from being distributed on their platforms. Campaigners have scrutinized this part of the legislation over concerns that it could amount to censorship, and argue that the use of copyright-protected material by way of commentary or parody should be permitted under the doctrine of "fair use." Particular attention has been paid to the status of "memes," which often rely on copyright protected images or pieces of video, and whether they could be censored as a result. "This plan for 'robo-copyright' would target memes, parodies and clips of people cheering at football matches," Jim Killock, executive director of anti-censorship organization Open Rights Group, told CNBC in an email Tuesday. "Copyright is important, but so is free speech." He added: "Machines can't judge human culture. When they can, we'll have bigger issues to think through than copyright enforcement." But Axel Voss, a European parliamentarian and key proponent of the law, has said it won't lead to the censorship of memes. "If we are looking to memes, the legitimate use of memes is not a question of Article 13, it is of copyright," Voss told CNBC in July. "This is nothing new."

Another controversial section is Article 11, which would grant news outlets a claim to copyright over the sharing of their content online. Opponents of the law, like Julia Reda, a European lawmaker and German Pirate Party politician, see this as an effective "link tax." But proponents, like Voss, say hyperlinks aren't under threat.

Why does it matter?

It's important to remember that internet giants such as Google are opposed to the law as it would impact their business model. The company has been accused of lobbying aggressively to prevent the directive from being passed into law. Many tech platforms, like Google's YouTube, rely on a model of user-generated content, where people often share images, music and snippets from films. In most cases, where a copyright infringement has taken place, content is taken down following a request from a publisher. But the new legal framework would place the onus of removal on internet giants. Such a shift in the law could force many of these firms to rethink that model. YouTube has said it is opposed to the law on the basis it could stifle the creative freedom of video makers and impact negatively on their subscriber bases and incomes. "We've always believed there's a better way than this, and that innovation and partnership are the keys to successful, diverse and sustainable news and creative sectors in the EU," the company said in an emailed statement. "For both European creators and consumers, it's vital to preserve the principles of linking, sharing and creativity on which so much of the web's success is built."

Julia Reda, German member of the European Parliament. Thierry Tronnel | Corbis Historical | Getty Images