Sen. Mike Lee again accused top executives of Google, Facebook and Twitter of bias against conservatives in how they block or moderate content — and then reveled when two of the three could not come up with, at his urging, any specific example of flagging or blocking a liberal group’s content.

So Lee tweeted after a Senate Commerce Committee hearing on Wednesday, “Big Tech suppresses #ProLife groups all the time but can’t name one time they suppressed Planned Parenthood, NARAL, or Emily’s List.”

That came during a hearing that questioned tech company chief executives Mark Zuckerberg of Facebook, Jack Dorsey of Twitter and Sundar Pichai of Alphabet, Inc., the parent company of Google. Lee participated via internet from Arizona, where he was campaigning for President Donald Trump.

The three tech companies insist their policies treat all sides fairly in fact-checking, flagging questionable content or blocking it. But Lee and other conservatives disagreed.

“You seem to do the opposite and take censorship related actions against the president, against members of his administration, against the New York Post, the [satire site] Babylon Bee, the Federalist, pro-life groups and there are countless other examples,” Lee said.

“Have you ever censored a Democratic senator? How about President Obama? How about a Democratic presidential candidate? How about Planned Parenthood or NARAL or Emily’s List?” he asked. “Can you name for me one high-profile person or entity from a liberal ideology who you have censored?”

Zuckerberg with Facebook was asked first and said he would need time to think about it and provide a list.

I’m just asking you if you can name for me one,” Lee asked, and Zuckerberg again said he needed to think about it.

Dorsey with Twitter similarly said he could later provide an “exhaustive list.” Lee again said, “I’m asking for a single example. One just one individual. One entity. Anyone.”

Dorsey said Twitter had taken action against two Democratic House members, but couldn’t immediately name them but promised to provide the information later.

Pichai with Google was able to name several liberal groups whose ads had been moderated or removed, including Democratic candidate Joe Biden. “We have taken down ads on both sides of the campaign” because of violent content, he said.

Lee told the trio, “Given the disparate impact of who gets censored on your platforms, it seems that you’re either one, not enforcing your terms of service equally, or alternatively, two, that you’re writing your standards to target conservative viewpoints.”

Zuckerberg pushed back.

“Our principle is to stand for free expression and to be a platform for all ideas,” he said. “I certainly don’t think we have any intentional examples where we’re trying to enforce our policies in a way that is anything other than fair and consistent.”

He added that all the companies have had complaints from both liberals and conservatives that they are unfairly targeted.

Lee has scolded social media giants on the topic numerous times in recent months. He has tangled the possibility of breaking up their possibly monopolies as chairman of the Senate Judiciary Antitrust Subcommittee, which oversees legislation about monopolies.