Mark Zuckerberg testifies before the House Energy and Commerce Committee in the Rayburn House Office Building on Capitol Hill April 11, 2018. Chip Somodevilla | Getty Images

Britain just announced plans for a tough new law aimed at forcing tech giants like Facebook and Twitter to clean up their platforms. The rules, unveiled in a white paper on Monday, would impose a legally binding duty of care on social networks to make sure they tackle harmful content. A new industry-funded regulator will be introduced under the proposals. It could have the power to slap internet firms with heavy fines, block people's access to websites and potentially hold executives personally liable for violations. U.K. Culture Secretary Jeremy Wright said the new policy would put an end to the "era of self-regulation for online companies." "Voluntary actions from industry to tackle online harms have not been applied consistently or gone far enough," he said in a statement Monday.

Why does it matter?

The new rules call on social media companies to effectively make sure their users are protected from harmful content. That includes: Child abuse

Terrorist content

Cyberbullying and trolling

Encouraging self-harm and suicide

Disinformation And those types of content fall within two key categories the government has defined: content that is illegal — like terror and child abuse — and content that is harmful but might not necessarily be illegal — like cyberbullying and disinformation. Critics argue the proposals could lead to censorship. Jim Killock, executive director of pro-internet freedom organization Open Rights Group, says those definitions create a "potential for misjudgment" that could inevitably result in the takedown of posts that aren't actually harmful. "This has potential for a lot of overreaction, incentivizing removal of a lot of legal content," he told CNBC. "There is a complete absence of discussion about how and why free expression gets entangled with any of those issues."

The U.K. government argues that new regulation is needed to keep internet users — minors in particular — safe. "For too long these companies have not done enough to protect users, especially children and young people, from harmful content," British Prime Minister Theresa May said in a statement Monday. "Online companies must start taking responsibility for their platforms, and help restore public trust in this technology," she added. Britain also says the new laws won't infringe on privacy and freedom of expression.

Impact on Big Tech