General Electric Co. engines powering as many as 150 Boeing Co. 787 jets world-wide are susceptible to sudden in-flight shutdowns due to internal ice accumulation, prompting U.S. regulators to order swift fixes to eliminate the danger.

A Federal Aviation Administration safety directive released this week indicates that certain upgraded models of General Electric’s most advanced engine pose an unacceptable safety risk because internal ice buildup—detected in one recent incident at an unexpectedly low altitude—could result in...