Mark Zuckerberg's refusal to appear in front of a parliamentary inquiry into the alleged abuse of Facebook users' data has been described as "absolutely astonishing" by MPs.
The Facebook founder has offered to send senior executives in his place to give evidence to a Commons committee.
Damian Collins, chairman of the digital, culture, media and sport committee, said: "I would certainly urge him to think again if he has any concern for the people who use his company's services."
He described the questions that MPs have as of "fundamental importance to Facebook users as well as to our inquiry" – and said the seriousness of the allegations meant it was "appropriate" for Mr Zuckerberg to appear in person or via video link.
Mr Collins' remarks came as a parliamentary meeting heard evidence on the alleged illicit transfer of Facebook users' data by Cambridge Analytica (CA).
The committee asked whistle-blower Christopher Wylie to tell them what he knew about the company, which allegedly used data gathered from Facebook users in targeted messages on behalf of Donald Trump's presidential campaign.
Mr Wylie claimed that the suspended chief executive of CA, Alexander Nix, had not been truthful to the committee when he claimed his company did not use Facebook data.
He said he also believed that AggregateIQ – a Canadian company that is closely linked to CA – played a "very significant" role in securing the UK's vote to leave the European Union in 2016.
Facebook's founder and chief executive was sent a formal request to appear before MPs and answer questions regarding a growing scandal about user data last week.
The company has offered to send chief technology officer Mike Schroepfer or chief product officer Chris Cox to Parliament next month to provide answers.
The hearing took place just as the EU's justice commissioner Vera Jourova wrote to Facebook with her questions regarding the scandal. The EU has given Facebook a two-week deadline to respond.