In a move that heralds a growing effort to check the power and influence of Big Tech, President Biden on Tuesday appointed Lina Khan, a top antagonist of the tech industry, to chair the Federal Trade Commission, the federal government’s primary antitrust watchdog.

Biden’s decision to put Khan in charge of the FTC’s agenda is the clearest sign yet that his administration will take a drastically different approach to regulating the tech giants than did President Barack Obama, whose administration took a largely hands-off approach toward Silicon Valley.

Reaction from both supporters and detractors reflected that expectation.

Sen. Elizabeth Warren (D-Mass.), who launched her failed presidential campaign pledging to break up the tech companies, hailed the move as “a huge opportunity to make big, structural change by reviving antitrust enforcement and fighting monopolies that threaten our economy, our society, and our democracy.”

Critics were equally adamant.

“Lina Khan’s antitrust activism detracts from the Federal Trade Commission’s reputation as an impartial body that enforces the law in a nondiscriminatory fashion,” the tech industry group NetChoice, which counts Amazon, Facebook and Google among its members, said in a statement. It described itself as “disheartened” by the development.

News of Khan’s elevation to the top spot at the FTC came shortly after the Senate, in a rare show of bipartisanship, confirmed her appointment to a seat on the five-member commission on a vote of 69 to 28. Twenty-one Republicans joined 46 Democrats and two independents in backing Khan — another signal of the growing bipartisan interest in reining in tech companies’ power. Sens. Charles E. Grassley (Iowa), the top Republican on the Judiciary Committee, and Roger Wicker (Miss.), the top Republican on the Commerce, Science and Transportation Committee, were among her supporters.

Khan, 32, is known for her unconventional proposals to counter the tech giants’ power. While still in law school in 2017, she wrote a paper denouncing Amazon for what she said was anti-competitive behavior and suggesting U.S. anti-competition laws were poorly equipped to counter the world of e-commerce. (Amazon founder and CEO Jeff Bezos owns The Washington Post.)

She later served as counsel to a House investigatory panel that last year issued a report detailing what it said were the tech companies’ anti-competitive behavior. She is now an associate professor at Columbia Law School and previously worked as a legal adviser to FTC Commissioner Rohit Chopra (D). She will be one of the youngest commissioners in the FTC’s history.

Biden’s decision to name Khan chair, which was announced by Sen. Amy Klobuchar (Minn.) at the beginning of a Senate hearing with tech executives Tuesday, was unexpected. As a candidate, he did not go as far as other liberal Democrats in calling for regulation of Amazon, Facebook, Google and other tech giants.

Klobuchar, another moderate Democrat who has advocated for broad reforms to U.S. competition law, said in an interview that she didn’t agree with all of Khan’s positions. But she called Khan’s elevation to FTC chair “exciting news.”

“I think she is an out-of-the-box thinker, someone who will look at these things in the forward-looking way we need to look at tech today,” Klobuchar said.

The mood in Washington favors action against the tech giants. Only last week, House lawmakers from both parties unveiled bills that could force Silicon Valley companies to change their business practices and in the most severe cases, break up the companies. Those proposals were the result of the House investigation into the tech giants that Khan helped lead. The probe found monopoly-style tactics and anti-competitive behavior at Facebook, Google, Apple and Amazon.

Khan tweeted Tuesday that she looked forward to upholding the FTC’s mission “to safeguard fair competition and protect consumers, workers and honest businesses from unfair & deceptive practices.”

During her confirmation hearing, she signaled she would take a tough line on regulating tech giants. She said that in the past few years, new evidence has come to light showing there were “missed opportunities” for enforcement actions against tech companies under the Obama administration. She also said new findings show the FTC must be “much more vigilant” when it comes to large acquisitions in digital markets.

Khan also said she was particularly concerned about the ways in which large companies use their dominance in one market to give them an upper hand in others, an issue under intense scrutiny by Congress.

Khan is one of several critics of Big Tech that Biden has brought into his administration. Tim Wu, who has called for antitrust action against the tech giants, works on competition and technology policy on the National Economic Council. Vanita Gupta, who has criticized big tech’s civil rights record, is now associate attorney general at the Justice Department.

But Biden has yet to put forth nominees for other key tech enforcement positions in the administration, and it’s unclear if he will elevate people more aligned with Khan or more business-friendly Democrats. Nearly five months into his term, Biden has not yet announced his nominee for the top spot in the Justice Department antitrust division or to fill a vacancy at the Federal Communications Commission.

Khan’s arrival at the FTC gives Democrats a 3-2 majority as she joins Chopra and Rebecca Kelly Slaughter, who was serving as acting chair. But Chopra is awaiting a Senate vote on his nomination to lead the Consumer Financial Protection Bureau. If he’s confirmed, Biden would have another FTC vacancy to fill, and until then the commission would be deadlocked between Democrats and Republicans.

Liberal groups Tuesday ratcheted up pressure on Biden to fill the vacancies in the wake of Khan’s confirmation.

“Lina Khan alone cannot bring in a new age of American trustbusting,” said Jeff Hauser, executive director of the Revolving Door Project, which scrutinizes the corporate ties of government officials.

Khan is joining the agency amid growing concerns over whether it has adequate powers and resources, particularly to take on technology giants. Her arrival comes at a critical moment: The agency last year brought a historic antitrust lawsuit against Facebook, and it is under pressure to bring a similar challenge against Amazon.

Yet lawmakers and tech experts have broadly raised concerns about the agency’s track record on enforcing existing laws against the tech giants. Democrats slammed the agency’s record-setting $5 billion privacy settlement with Facebook in the wake of the Cambridge Analytica scandal as a slap on the wrist for the company, and they said it underscored the need for new privacy and consumer protection laws. The agency faced similar criticism later that same year, when it reached a $170 million settlement with Google over allegations the company illegally collected data about children under age 13.

Advocates for greater enforcement of antitrust law said Khan’s confirmation could signal a turning point for the agency, after what they say have been decades of inaction since the Reagan administration.

Khan can “chart a wholly different approach,” said Sarah Miller, executive director of the American Economic Liberties Project. “The chair has significant authority over the direction of the agency.”

There’s growing bipartisan support to expand the agency’s resources. The Senate recently passed a bill that would increase funding for the agency by overhauling merger filing fees, and House lawmakers introduced similar legislation as part of their package targeting large tech companies.

Shortly after Khan’s confirmation Tuesday, the Senate Judiciary Committee antitrust panel hosted a hearing on competition issues related to connected home devices. Executives from Sonos, Apple and Google testified, as well as academics.

Klobuchar, the panel’s chairwoman, said in opening remarks that it’s important for lawmakers to stay ahead of new competition issues in the tech industry. “We have this moment with this kind of technology to look around the corner and see ahead,” she said.

Geoffrey A. Fowler contributed to this report.