WASHINGTON — The chair of the Federal Trade Commission defended her aggressive legal strategy toward the country’s biggest technology companies Thursday as House Republicans charged that the agency has become overzealous and politicized under President Joe Biden.

Republicans charged that Lina Khan is “harassing” Twitter since its acquisition by Elon Musk, arbitrarily suing large tech companies and declining to recuse herself from certain cases. In April, the committee subpoenaed Khan after an investigation by the panel concluded the agency went after Musk for political reasons.

Khan pushed back on the criticism, arguing that more regulation is necessary as the companies have grown and that tech conglomeration could hurt the economy and consumers.

“Our competition mission is driven by the tenet that vigorous antitrust enforcement is critical to the growth and dynamism of our economy, as well as to our shared prosperity and liberty,” Khan said. “Recent decades, however, have vividly illustrated how Americans lose out when markets become more consolidated and less competitive.”

The hearing comes as the agency has been embroiled in several legal cases against technology companies and as Khan — an outspoken critic of Big Tech before becoming the agency’s head — has tried, not always successfully, to toughen government regulation of those companies and prevent them from growing any larger.

Khan and the agency suffered a major defeat Tuesday when a federal judge declined to block Microsoft’s looming $69 billion takeover of video game company Activision Blizzard. The FTC had sought to ax the deal, saying it will hurt competition.

U.S. District Judge Jacqueline Scott Corley said the deal, the largest in the history of the tech industry, deserved scrutiny but the FTC hadn’t shown that it would cause serious harm. The FTC is appealing her ruling.

In a similar case, another judge rebuffed the FTC’s attempt earlier this year to stop Meta from taking over the virtual reality fitness company Within Unlimited.

Republicans focused on the agency’s poor legal record on those antitrust cases. “Are you losing on purpose?” asked Rep. Kevin Kiley, a California Republican, citing a past comment from Khan that suggested courtroom losses would signal to Congress that it needs to update its antitrust laws.

“Absolutely not,” Khan replied, while acknowledging that “unfortunately, things don’t always go our way.”

Republicans questioned the wisdom behind aggressive regulation, and whether it could hurt small businesses as well.

California Rep. Darrell Issa criticized the FTC’s “left turn” since she took over two years ago.

The FTC has also sued Amazon for allegedly engaging in a yearslong effort to enroll consumers without consent into Amazon Prime and making it difficult for them to cancel their subscriptions.

In a complaint filed in federal court last month, the agency accused Amazon of using deceptive designs, known as “dark patterns,” to deceive consumers into enrolling in the service.

In addition, Khan and other FTC officials have repeatedly warned they will also crack down on harmful business practices involving artificial intelligence, in messages partly directed at the developers of AI tools such as ChatGPT.

Much of the Republicans’ focus has been on the FTC’s actions toward Twitter, which the agency has been investigating as part of ongoing oversight into the social media company’s privacy and cybersecurity practices. The GOP lawmakers noted that the agency probe included efforts this spring to obtain Musk’s internal communications and information about journalists.

House Judiciary Committee Chairman Jim Jordan, R-Ohio, said that Khan’s oversight of Twitter seems like an “obsession.”

“Why are you harassing Twitter?” Jordan asked.

Khan said the agency has been focused on Twitter’s lax security and privacy policies and noted that the agency has been investigating the platform for years, since before Musk’s tenure.

The FTC has been watching the company since Twitter agreed to a 2011 consent order alleging serious data security lapses. But the agency’s concerns spiked with the tumult that followed Musk’s October takeover of the company.