WASHINGTON—Chiefs of the largest social-media companies tangled with U.S. lawmakers Friday at one of the most anticipated congressional hearings on potential government pressures on the margins of the Internet—detailing what kind of unchecked testimonials weigh heavily on the strength of tailored advertising.

The events underscored the contradiction between the bipartisan response to a White House request for data on political advertising that Senate Intelligence Committee Chairman Richard Feinstein (D-Calif.) expected to include a few honchos representing the modern online world with some dissenting voices.

Partners for Traditional Media Respon­ded

Representatives from those companies sought to cast the Facebook co-founder, Mark Zuckerberg, several executives from Twitter, and Google's executive chairman, Eric Schmidt, as frequently addressing the part of the operation that delivers the general offering of news to users. The hearing, before the House Intelligence Committee, capped a four-year effort by the committee to gauge scrutiny that traces back years to the birth of the modern Internet, particularly for political-media companies.

"Given the new Internet, which, clearly, the face of social media campaigns is changing very quickly, any third party whose role it will be is out of sync with that experience," said Brad Burnham, a lawyer representing Facebook. Mr. Burnham was demonstrating another area in which the companies are under greater scrutiny: how much contributed content runs alongside crowdsourced expressions of political opinion that quickly get shared on Facebook or other current platforms.

Representatives from Google said that they "frustrated" in their discussions with the Federal Bureau of Investigation about what exactly was triggering company notices about criminal or terrorist activities related to social-networking technology.

"I can't put Google black letters on our responsibility however minor" to detect copyright infringement of copyrighted content, said Heather Austin, head of Google's enforcement policies. But she did say Google was concerned that compliance with requests for digital fingerprints would "jeopardize our legal system and hurt Internet freedom" by implying them could be assumed as a basis to seize Americans' communications in court.

Mr. Feinstein's contrition over the Facebook recommendation to his committee was greeted with derision by conservatives who have called out Facebook for encouraging shocking, vitriolic political speech that had nearly of 911live.com threads about the Charleston killings and calls for the mass slaughter of fellow Christians as witness who dispute that President Barack Obama is a Christian, as well as terrorist content that seems to have Muslim strongholds as witnesses.

The Tests of Diversity

The issue was one that President Barack Obama raised in a Facebook post Friday to explain
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