But investors shouldn't worry much about potential fallout, Bob Peck, head of internet investment banking at Credit Suisse, said Tuesday.
"It's very important and very serious," Peck told CNBC's "Squawk Alley," "but as far as impacts to the financials, not as significant."
Facebook said Monday that Russian-bought election content reached 126 million Americans, but as Peck noted, that's out of a "2 billion or so base."
Google, for its part, was fined $2.7 billion by the EU in June for advertising antitrust violations.
But, Peck said, $2.7 billion on a market cap of more than $700 billion isn't likely to move the needle.
"Don't forget the way these models work in advertising — Google and Facebook — it's an auction basis, so as one large bidder drops out, the rest of the market sort of fills that," Peck said.
To be sure, the week's hearings could still represent a turning point for the internet giants as discussions of foreign influence and regulation continue to swirl. Twitter and Facebook have each moved to increase transparency around advertising, after public comments by CEOs Jack Dorsey and Mark Zuckerberg.
The hearings could signal whether Congress intends to more strictly oversee these companies in the future, but even that wouldn't impact financials or scare investors, Peck said.
Facebook stock is up 37 percent on the year. Google is up 27 percent and Twitter more than 15 percent.