WASHINGTON— Amazon.com Inc. filed a request with the Federal Trade Commission seeking the recusal of new Chairwoman Lina Khan from antitrust investigations of the company, in light of her extensive past criticisms of the online giant.

“Given her long track record of detailed pronouncements about Amazon, and her repeated proclamations that Amazon has violated the antitrust laws, a reasonable observer would conclude that she no longer can consider the company’s antitrust defenses with an open mind,” Amazon said in a 25-page motion filed Wednesday with the FTC.

An FTC spokeswoman declined to comment.

Ms. Khan has been a leading critic of dominant technology companies—especially Amazon—and a central figure in a progressive movement that favors sweeping changes to antitrust enforcement to take on the nation’s most powerful firms. The Senate confirmed her earlier this month for the FTC, and President Biden immediately installed her as the head of the agency.

Amazon’s recusal request comes at a pivotal time both for the company and the FTC.

The commission has an open, wide-ranging antitrust investigation into Amazon’s business practices, and it recently secured the right to review Amazon’s proposed acquisition of Hollywood studio MGM.

The five-member FTC currently has a 3-2 Democratic majority.

Commissioners have found bipartisan agreement on a range of matters but have split in some high-profile antitrust cases, and the commission’s two Republicans hold views that diverge from Ms. Khan’s.

Ms. Khan’s career took off after she wrote a widely read law-review article while a student at Yale Law School that argued that antitrust law has failed to restrain Amazon.

Before her nomination to the FTC, Ms. Khan worked as a key House staffer on a congressional antitrust panel that conducted a 16-month investigation of large online platforms and last year recommended that lawmakers take steps to rein them in.

During Ms. Khan’s confirmation proceedings, Sen. Mike Lee of Utah, a leading Republican on antitrust issues, asked her whether she would have to recuse herself from Big Tech cases because of her work on the House online-platform investigation.

Ms. Khan said she would consult with FTC ethics officials if recusal questions arose.

Write to Brent Kendall at brent.kendall@wsj.com