(CNN Money) -- Mark Zuckerberg took heat from members of Congress Wednesday over illegal opioid sales on Facebook.
Rep. David McKinley, a Republican from West Virginia, was one of those who pressed Zuckerberg on why Facebook hasn't done more to remove posts from sellers offering illicit opioids.
"Your platform is still being used to circumvent the law and allow people to buy highly addictive drugs without a prescription. With all due respect, Facebook is actually enabling an illegal activity and in so doing, you are hurting people. You'd agree with that statement?" he asked.
Critics have called out tech companies for not doing enough to crack down on illicit drug sales on their platforms. The issue isn't exactly new. In 2011, Google agreed to pay $500 million to the Department of Justice for showing prescription drug ads from Canadian online pharmacies to U.S. consumers. It stopped the practice in 2009 once it became aware of an investigation by a U.S. Attorney's office.
But sellers are still finding ways of posting about drug sales on platforms like Facebook and Instagram, which critics have accused of being reactive, largely waiting for activists, or the press, to surface issues and help police their platforms.
Content removal across tech platforms has largely been a game of whack-a-mole. Just last week, one woman, Eileen Carey, pushed a Facebook executive to remove "#Oxycontin," among other terms, from Instagram, the photo sharing app owned by Facebook. Carey told CNN that she reached out directly to the exec after failed attempts at flagging the content within the Instagram platform.
Responding to McKinley, Zuckerberg circled the issue by talking about how the company needs to build more artificial intelligence tools. For now, he said, the company largely relies on its security and content reviewers to take down posts that are flagged by users. He has said that it will have 20,000 people in those roles by the end of the year.
"What we need to do is build more A.I. tools that can proactively find that content," Zuckerberg said.
McKinley held Zuckberg's feet to the fire: "You know that they're up there, where's your accountability?"
Zuckberg said that even 20,000 people can't look at all the content on the platform.
At other points in his congressional testimony, Zuckerberg claimed that Facebook has AI systems that can identify and take down 99% of ISIS content before people even see it.
Zuckerberg didn't provide any timeline for when similar tools might be rolled out to help with identifying drug sales on its platforms.
Meanwhile, overdose deaths from prescription and illicit opioids have doubled over the past six years alone -- from 21,089 deaths across the nation in 2010 to 42,249 in 2016.
Rep. John Carter, a Republican from Texas, also brought up the opioid epidemic in questioning Zuckerberg, asking him whether he was aware of various statistics related to the scale of the issue.
Zuckerberg has mused on the gravity of the issue before.
Five months ago, he said that the "biggest surprise" during his recent travels around the US was seeing the "extent of opioid issues."
Last week, FDA commissioner Scott Gottlieb specifically called out tech outlets like Facebook and Facebook-owned photo app Instagram for not "taking practical steps to find and remove these illegal opioid listings."
Zuckerberg said he wasn't "specifically aware" of Gottlieb's comments, "but I heard he said something."
When Carter mentioned that Gottlieb was planning to meet with tech representatives on the issue, Zuckerberg said: "I will be sure that someone is there."
© Copyright 2018 CNN. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.
for more features.