OTTAWA -- A panel of international politicians vented anger at Mark Zuckerberg and Sheryl Sandberg on Tuesday after the Facebook executives snubbed their summons to appear at the international grand committee on big data, privacy and democracy in Ottawa.

The committee's chair, Conservative MP Bob Zimmer, called it "abhorrent" the two did not appear, and he closed a marathon session of testimony by telling the two Facebook employees who were sent in their place that it was "shameful" their bosses didn't show up.

The committee, comprising politicians from Canada, Britain, Argentina, Belgium, Brazil, France, Ireland, Latvia, St. Lucia, Ecuador and Singapore, is examining the role of internet giants in safeguarding privacy and democratic rights. Zuckerberg and Sandberg were called to testify but did not appear.

Representatives of Twitter and Google also testified, but it was Facebook's two corporate pinch-hitters who drew the wrath of committee members.

Their collective frustration grew as Kevin Chan and Neil Potts, Facebook global policy directors, separated by two empty chairs bearing Zuckerberg and Sandberg's names, were grilled about past company conduct, including its decision this week to permit postings of a doctored video meant to portray U.S. House Speaker Nancy Pelosi as slurring her words, addled or possibly drunk.

The video was labelled false, and users were made aware of that classification, Potts said.

"This sets a very dangerous precedent," said British MP Damian Collins, the committee's co-chair.

Edwin Tong, a Singapore MP, clashed with Potts over how Facebook responded to postings from last fall that heralded the violence that came to pass in the Easter Sunday suicide-bomb attacks on three churches in Sri Lanka that left 250 dead.

"Let me suggest to you that you don't remove it because such content, being sensational, inciting fear, violence, hatred, conspiracy theories ... is what drives eyeballs to your platform -- this is what drives users to your platforms, and that is the engine room of your profit mechanism," said Tong.

Potts shot back: "Mr. Tong, I reject the premise."

Some MPs questioned why Zuckerberg meets world leaders behind closed doors, but chooses to send other officials from his company to field the public questions of lawmakers at the committee. His and Sandberg's absence on Tuesday has only fuelled skepticism about Facebook's promises to operate in a transparent manner.

New Democrat Charlie Angus said the pair's absence showed disrespect to legislators around the world.

"Facebook has serious responsibilities in terms of the misuse of the platform that has led to mass killings in Myanmar, the undermining of electoral systems around the world, the attack on private rights and citizen rights," he said.

"Mr. Zuckerberg has stated his willingness to work with legislators but he seems to blow us off whenever it seems we want to ask him questions."

The MPs, led by Angus, voted to serve a summons on the pair, compelling them to appear before the group the next time either sets foot on Canadian soil.

"As soon as they step foot -- either Mr. Zuckerberg or Ms. Sandberg -- into our country they will be served and expected to appear before our committee," said Zimmer.

If they refuse, he added, they will be held in contempt. It was not clear exactly what consequences that might have.

Jim Balsillie, the former chief executive of Research In Motion, which invented the BlackBerry smartphone, testified earlier Tuesday that a "toxic" social media business model is a threat to democracy.

Balsillie also offered a thinly veiled criticism of Zuckerberg and Sandberg for not responding to the committee's summons to testify.

"By displacing the print and broadcast media in influencing public opinion, technology is becoming the new fourth estate. In our system of checks and balances, this makes technology co-equal with the executive, the legislative, and the judiciary," he said.

"When this new fourth estate declines to appear before this committee -- as Silicon Valley executives are currently doing -- it is symbolically asserting this aspirational co-equal status ... The work of this international grand committee is a vital first step towards redress of this untenable current situation."

Balsillie, now the chair of the Ontario-based Centre for International Governance Innovation, said technology, if left unchecked, will displace print and broadcast media, and he urged a panel of politicians to impose restrictions on big internet companies.

"Social media's toxicity is not a bug -- it's a feature," he told the committee, kicking off the second of three days of meetings in Ottawa aimed at figuring out how best to protect citizens' privacy and democratic fairness in the age of social media.

Federal privacy commissioner Daniel Therrien told the committee that "freedom and democracy cannot exist without privacy and the protection of our personal information."

Therrien last month concluded that Facebook violated Canadian privacy laws by failing to ensure political consultancy Cambridge Analytica got clear consent to use individuals' personal information. He is going to court to force Facebook to comply with privacy laws.

Cambridge Analytica allegedly gained improper access to some 87 million Facebook users' personal information and used it to try to influence the outcome of the 2016 U.S. presidential election and the Brexit referendum in the U.K. Therrien said the scandal "reminded citizens that privacy is a fundamental right and a necessary precondition for the exercise of other fundamental rights, including democracy."

Ellen Weintraub, chair of the U.S. Federal Election Commission, recounted the "chilling" evidence of sweeping and systemic Russian interference in the 2016 American election, hacking into computer systems and using fake news and phoney social media accounts to bolster Donald Trump's campaign, exacerbate societal divisions and undermine Americans' faith in democracy.

"Facebook's originating philosophy of 'move fast and break things,' cooked up 16 years ago in a college dorm room, has breathtaking consequences when the thing they're breaking is our democracies themselves," she said.

This week's meeting of the grand committee -- the second since last year's inaugural gathering in Britain -- is being hosted by the House of Commons committee on access to information, privacy and ethics.