WASHINGTON, Jan 20 (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 ( AMZN ), opened an

investigation into Microsoft ( MSFT ), and won court rulings

that blocked Kroger's ( KR ) $25-billion acquisition of rival

grocery chain Albertsons ( ACI ) 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 ( AMZN ) 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.