Rep. Joe Barton, a Texas Republican, held up his phone and told Zuckerberg he was going to ask him a question that someone had submitted to the congressman's Facebook account.
'First question: Please ask Mr. Zuckerberg, why is Facebook censoring conservative bloggers such as Diamond and Silk? Facebook called them "unsafe" to the community. That is absurd. They hold conservative views. That isn't unsafe,' Barton said reading the question, and adding his own, 'What's your response?'
Zuckerberg explained that his team had made 'an enforcement error.'
'And we've already gotten in touch with them to reverse it,' he said, referring to Diamond and Silk.
Another Congressman, Rep. Fred Upton, a Republican from Michigan referred to the video bloggers as 'Silk and Diamond' and then asked about an incident involving a GOP political candidate from his state who expressed pro-life views, and whose message was deemed a 'threat' by Facebook.
'I'm not sure what the threat was when I read the post,' Upton said.
Zuckerberg said he was unfamiliar with that particular case.
'Unfortunately, we don't always get these things right,' the CEO told the lawmakers, adding that Facebook has 20,000 people to review content posted.
Later on in the hearing on Wednesday, Rep. Marsha Blackburn, a Tennessee Republican running for Senate, asked whether free speech is being curtailed by the site.
Zuckerberg brought up terrorism as an example of content that would be banned.
'Let me tell you right now, Diamond and Silk is not terrorism,' Blackburn muttered at the end of her time.
Yesterday it was Sen. Ted Cruz who slammed Zuckerberg, accusing the social media platform of being politically biased.
'There are a great many Americans who I think are deeply concerned that Facebook and other tech companies are engaged in a pervasive pattern of bias and political censorship,' Cruz said. 'There have been numerous instances with Facebook.'
Cruz, a former GOP presidential candidate, then brought up Diamond and Silk.