United Airlines Holdings Inc. expects to shrink its management and administrative ranks by at least 30% starting in October, according to a memo sent to employees Monday, as the coronavirus pandemic wreaks havoc on the airline industry.

That amounts to at least 3,450 people — the first indication of how many are likely to lose their jobs as United UAL, -5.10% and other airlines grapple with a steep decline in air travel and an uncertain path to recovery.