U.K. lawmakers sent a letter to Facebook CEO Mark Zuckerberg Wednesday asking for clarification on whether he would eventually appear in front of them, after the social network agreed to send two of his deputies instead.
Last week, Damian Collins, the chair of the British parliament's Digital, Culture, Media and Sport Committee, asked Zuckerberg to appear in front of lawmakers to "give an accurate account of this catastrophic failure of process" related to the Cambridge Analytica data scandal.
A quiz app harvested 50 million Facebook profiles for data which were then sent over to Cambridge Analytica, a firm that was caught claiming it handled the digital aspects of President Donald Trump's 2016 election campaign.
Instead of Zuckerberg, Facebook said it would send either its Chief Technology Officer Mike Schroepfer or Chief Product Officer Chris Cox, to appear in front of U.K. lawmakers.
On Wednesday, Collins said he accepted the offer of evidence from Cox, and suggested the Facebook executive answer U.K. lawmakers' questions on April 24.
"However, given the seriousness of these issues we still believe that Mark Zuckerberg himself is the right person to give evidence," he said in a letter to Rebecca Stimson, Facebook's head of public policy.
"Mr Zuckerberg has stated in interviews that if he is the right person to appear, he will appear. He appears to have acted on this belief with respect to appearing before Congress. We now request confirmation as to whether he will make the same decision for us."
Collins has given Zuckerberg until April 9 to respond.
In an interview with CNBC earlier on Wednesday, Collins said he wasn't clear if this meant that Zuckerberg wouldn't come at all.
"We think these issues are so serious and they effect not just the way individual products work, but the culture of the company, its attitude towards the data of the users who use the platform, that the most appropriate person is the person who, in a way, is the kind of beating heart of the company, its founder Mark Zuckerberg," Collins said.
"So we would still like him to come. We will be writing to him today just to confirm, is he declining to attend or would he be prepared to come? Because in the company's response, it wasn't clear whether he was actually declining to attend, (or) merely suggesting someone else in his place."
The move would step up the pressure on Zuckerberg and Facebook's senior management who were criticized for responding slowly when the story first broke. Zuckerberg will reportedly testify before Congress, however.
Separately, in a letter to ousted Cambridge Analytica boss Alexander Nix, Collins requested Nix appear before U.K. lawmakers for questioning on April 17. In a screened expose by U.K. broadcaster Channel 4 last week, Nix was filmed saying on camera that Cambridge Analytica ran President Donald Trump's digital and television campaign.
—CNBC's Ryan Browne contributed to this report.