U.S. airlines warn 5G interference could compromise key safety systems and result in suspended passenger and cargo flights.
President Joe Biden, speaking to reporters on Monday, declined to say whether he endorsed a vaccine mandate for domestic air travel. The president has previously said he did not consider them necessary.
Thousands of customers have been affected by the latest pandemic-driven travel disruptions since Christmas Eve, with airlines including United blaming a "nationwide spike in Omicron cases" in recent days.
"The nationwide spike in Omicron cases this week has had a direct impact on our flight crews and the people who run our operation," a United spokesperson said in an emailed statement.