WASHINGTON, Jan 20 (Reuters) - Lina Khan, who headed the

U.S. Federal Trade Commission under former President Joe Biden

until Monday, will resign from the commission in the coming

weeks, she told staff in a memo.

Khan was an aggressive enforcer of antitrust law,

challenging numerous mergers and 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. 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.