European officials are seizing on disclosures from Facebook whistleblower Frances Haugen to accelerate and sharpen their plans to impose sweeping new restrictions on big technology companies.

After a series of meetings with Ms. Haugen, policy makers and lawmakers for the European Union said that the bloc must move quickly to toughen and enact measures in a bill proposed last year that would impose stiffer obligations on social-media services. The bill, as currently drafted, would require large tech platforms to actively look...

European officials are seizing on disclosures from Facebook whistleblower Frances Haugen to accelerate and sharpen their plans to impose sweeping new restrictions on big technology companies.

After a series of meetings with Ms. Haugen, policy makers and lawmakers for the European Union said that the bloc must move quickly to toughen and enact measures in a bill proposed last year that would impose stiffer obligations on social-media services. The bill, as currently drafted, would require large tech platforms to actively look for and mitigate risks from content that is illegal, or face hefty fines.

“Europe is serious about regulating what still resembles a digital Wild West,” said Thierry Breton, the EU’s digital commissioner. He added that the EU must race to pass its package of tech legislation in the first half of 2022. “Speed is everything,” he said.

In a hearing before the EU parliament on Monday, lawmakers quizzed Ms. Haugen about the content of a set of internal Facebook documents, first detailed in The Wall Street Journal, that show the company is aware of ways its systems cause harm but has often been slow to address those issues and has played them down in public.

The documents have given ammunition to politicians in Europe and the U.S. to pursue new legislation seeking to reduce big tech companies’ power, potentially updating decades-old laws that have largely shielded social-media platforms from liability for their users’ activities.

In the U.S., such legislation has started to gain traction in Congress. In the U.K., lawmakers are considering a new bill on online safety, enforced by a regulator that could issue fines of up to 10% of annual global revenue. Meanwhile, the EU’s bill is currently under debate within the bloc’s parliament and among member-state governments, which would later have to settle on a common text.

In recent weeks, Ms. Haugen has met with British and German officials to push for new laws increasing transparency and regulatory oversight of how social-media companies handle content. She will come to Paris for similar meetings later this week. At each stop, Ms. Haugen has made the case that Facebook has done too little to limit the ways its system promotes polarizing and extremist content because such changes would undermine usage of its service.

Facebook has disputed Ms. Haugen’s assertions. “Yes, we’re a business and we make profit, but the idea that we do so at the expense of people’s safety or well-being misunderstands where our own commercial interests lie,” wrote Monika Bickert, the company’s vice president of content policy, in a blog post Monday. Facebook is owned by Meta Platforms Inc.

Members of Congress have likened Facebook and Instagram’s tactics to that of the tobacco industry. WSJ’s Joanna Stern reviews the hearings of both to explore what cigarette regulation can tell us about what may be coming for Big Tech. Photo illustration: Adele Morgan/The Wall Street Journal The Wall Street Journal Interactive Edition

Several EU legislators said the Facebook documents that Ms. Haugen disclosed showed the EU’s new-social media bill should go further than it does in its current draft. The lawmakers argued, for example, that the proposed Digital Services Act should tackle potentially harmful content that doesn’t violate any laws or should focus more on how companies recommend and spread content.

“My hope is that it’s going to strengthen the DSA and broaden the discussion to put the focus on the systemic risks and what we can do about it,” said Alexandra Geese, a Green Party member of the European Parliament who is involved in negotiations over the legislation. Ms. Geese says she hopes the whistleblower disclosures will boost momentum for stronger transparency requirements and enforcement than are currently in the bill. “The DSA must be ambitious and have teeth,” she said.

In Monday’s hearing Ms. Haugen said that the EU’s new social-media bill “has the potential to be a global gold standard” and to “inspire other countries, including my own, to pursue new rules that would safeguard our democracies.” But she added, echoing some legislators like Ms. Geese, that the legislation must avoid loopholes and would require strong central enforcement to be credible.

The documents Ms. Haugen disclosed were described in a series of Journal articles beginning in September that show, among other things, that Facebook knows its ranking algorithms foster discord and that Instagram can have negative effects on teenage girls’ mental health.

The Journal reported last week that company researchers found 1 in 8 Facebook users, or roughly 360 million people, report engaging in compulsive use of social media that impacts their sleep, work, parenting or relationships.

Write to Sam Schechner at sam.schechner@wsj.com