Facebook's boss accused of evasion while EP leaders' choice of format for question and answer session slammed as inadequate.
Facebook boss Mark Zuckerberg has faced criticism for not answering questions faced with the leaders of the European parliament on Tuesday.
With 44 minutes for questions, Zuckerberg's answers took 26 minutes. That was the allotted hour,
MEPs were furious over the format, which the European Parliament's president defended.
'Mr Zuckerberg is an American citizen. He was obliged to testify to the American parliament, he was not obliged to come here. Yesterday he presented his apologies," said Antonio Tajani.
Criticism came thick and fast, led by the Green-EFA coalition which accused Tajani of offering Zuckerberg the easy way out, while centrist Guy Verhofstadt and ALDE leader demanded written answers to fill in the many blanks he said Zuckerberg had left unfilled.
There is increasing concern at the vulnerability of social media networks to malicious electoral manipulation and the potential threat this poses to democracy. The EU wants to ensure that Facebook, which has more European than US members, raises its standards, and quickly.
Facebook's compliance with the new EU data rules will be closely watched, as will its efforts to tackle the spread of fake news ahead of European Parliament elections next year.
"Some sort of regulation is important and inevitable," Zuckerberg said, but he echoed calls in the United States that innovation should not be stifled.
Zuckerberg will go on to meet French President Emmanuel Macron on Wednesday but has so far declined to appear in front of British lawmakers.