WASHINGTON (Reuters) - Lina Khan, who until Monday was an aggressive enforcer of antitrust law as the head of the U.S. Federal Trade Commission under former President Joe Biden, will resign from the commission in the coming weeks, she told staff in a memo.

Khan challenged numerous mergers during her tenure, while working to ensure consumers and workers were not disadvantaged by powerful corporations.

Under Biden, Khan's FTC sued Amazon, opened an investigation into Microsoft, and won court rulings that blocked Kroger's $25-billion acquisition of rival grocery chain Albertsons and the $8.5 billion merger of handbag makers Tapestry and Capri.

The youngest person to lead the U.S. consumer protection and antitrust agency, Khan gained attention in 2017 when she wrote a paper arguing that Amazon had amassed monopoly power by undercutting competitor prices and harvesting consumer data.

Republican Commissioner Andrew Ferguson is now the agency's chair after President Donald Trump took office.

Some of Khan's agenda proved divisive.

A court struck down a broad ban on worker noncompete agreements aimed at allowing employees to launch competing businesses and spurring employers to compete harder for labor.

A rule that would require subscription services to offer simple cancellation methods also faces court challenges.

Ferguson and Melissa Holyoak, the other Republican on the commission, had voted against those rules as well as a recent case against an alcohol distributor that revived a long-dormant price discrimination law.

A source told Reuters on Monday that Khan plans to use her remaining time as a commissioner to complete document retention and records management as required by law, as well as other administrative tasks.