Figurines are seen in front of the Facebook logo in this illustration taken March 20, 2018. REUTERS/Dado Ruvic

BRUSSELS (Reuters) - EU leaders on Thursday urged social networks to guarantee transparent practices and fully protect personal information as pressure piled on Facebook after allegations that data from 50 million of its users was mishandled.

More than $50 billion (£35.4 billion) has been wiped off Facebook’s market value on reports that British political consultancy Cambridge Analytica improperly accessed data to build profiles on American voters and influence the 2016 presidential election.

“Social networks and digital platforms need to guarantee transparent practices and full protection of citizens’ privacy and personal data,” the European Union heads of state said in after meeting in Brussels. “EU and national legislation must be respected and enforced.”

The harvesting of user data happened before a new EU data protection law comes into force under which companies could be fined up to 4 percent of global turnover for violating.

“We cannot apply the sanctions which are coming with GDPR (General Data Protection Regulation) from May onwards,” EU Justice Commissioner Vera Jourova told reporters on Thursday.

In Britain, which is leading the investigation from the European side, the maximum sanction is 500,000 pounds ($705,000), Jourova said, an insignificant amount compared to Facebook’s $40.65 billion in revenue for 2017.

European Parliament head Antonio Tajani invited Facebook’s Chief Executive Mark Zuckerberg to come to the legislature to explain “how Cambridge Analytica came to use the personal data of millions of people to influence the... U.S. presidential elections and the Brexit referendum.”

On Wednesday Zuckerberg apologised for mistakes his company made and promised to restrict developers’ access to user information as part of a plan to improve privacy protection.

Jourova said more than one announcement would be needed to renew people’s trust in Facebook. “This is much more serious because here we witness the threat to democracy, to democratic plurality. It is endangering the free electoral choices of the people in Europe,” she said.