By Rebecca Heilweil

Updated at 5:24 p.m. ET

By the end of trading on Tuesday, shares in the largest U.S. tech firms bounced back. Tech stock prices had tumbled on Monday afternoon, following news that government agencies and lawmakers will investigate whether the companies have engaged in anti-competitive practices.

But after falling 7.5 percent yesterday, Facebook finished 2.5 percent higher today. Google's parent company Alphabet surged 1.5 percent, after Monday's 6.1 percent decline.

On Monday, it was widely reported that the Department of Justice and the Federal Trade Commission had [divvied up] ( their antitrust investigations. The DOJ will reportedly look into Google and Apple, while the FTC will probe Facebook and Amazon.

In a separate move, the House Judiciary Committee announced that it too would begin an antitrust investigation into several tech giants.

But a former FTC antitrust enforcer warns that it will take more than proving that these companies resemble monopolies to win any future case.

"It's pretty clear that they have a lot of power in the markets where they operate. But the agencies would also have to prove that these companies had actually done something wrong in order to bring an antitrust case. Just showing that they have a monopoly, or a near-monopoly, is not enough," Charlotte Slaiman, a former FTC antitrust enforcer and current policy counsel at the non-profit Public Knowledge, told Cheddar.

The House Judiciary Committee explained in a press release that its investigation will look into competition on online markets, whether tech firms have behaved in an anti-competitive manner, and the adequacy of current antitrust laws. "[I]t is vital for Congress to step in to determine whether existing laws are adequate to tackle abusive conduct by platform gatekeepers or if we need new legislation," said Rep. David Cicilline (D-R.I.) in a news release.

Public Knowledge, which focuses on intellectual property and competition in the digital world, [welcomed] ( news of the investigation.

Slaiman added that a "normal" antitrust investigation would take about a year, but that subsequent litigation could take another year, at minimum. "They're such large companies, there might be multiple forms of conduct that are being investigated," said Slaiman.

She added that remedies could go beyond fining or forcing divestitures (also known as a breakup), such as requiring companies to provide interoperability and data portability.

"Data portability is the ability to transfer your data one time. Interoperability is a continuous porting of the data," she explained. "So if I just wanted to take my Facebook profile information to a new social network, that's portability. But if I want to be able to communicate with my friends back on Facebook from the new social network, that's interoperability."

The U.S. follows in the lead of Europe, which has been aggressive about investigating and regulating tech giants, especially concerning issues of antitrust violations and data privacy.

"That's certainly something that makes the U.S antitrust agencies pay attention, but our law here is different," said Slaiman. "The U.S. antitrust laws are in some ways narrower than the EU antitrust laws. They require certain economic tests that are a little different, so it's going to be a whole new investigation if that's the type of thing the DOJ is interested in."

For full interview click here.