More people flew out of airports in the United States on Sunday — 2.46 million according to the Transportation Security Administration — than on any other day so far this year. The Fourth of July holiday is expected to be even busier, with Hopper, a travel booking app, predicting that nearly 13 million passengers will fly to, from and within the United States this weekend.

The question for many travelers is whether they can trust airlines to get them where they want to go on time.

Independence Day weekend is expected to be the second busiest for travel since 2000, with flight delays, cancelations and staffing woes.

Why it matters: It's a sign that the summer of "revenge travel" is upon us, with Americans splurging on travel and enduring delays to make up for pandemic-related cancellations.

The big picture: Airlines from coast to coast have been bracing for "operational challenges" this weekend, with some even encouraging customers to rebook their plans for another weekend.

Hundreds of flights were delayed or canceled Friday amid airline staff shortages and protests, as the Fourth of July travel rush got underway.

There were already more than 1,870 flight delays and 270 cancellations — well above the daily average of 210 scrapped flights — domestically as of noon Friday, according to the airline tracking service FlightAware.

More than 48 million people were expected to hit the road for the holiday weekend as airlines struggled to keep up with the soaring summer travel demand.

United Airlines and Delta Air Lines (DAL.N)have canceled hundreds of Christmas Eve flights, as the spreading COVID-19 Omicron variant takes a toll on its flight crews and other workers.

Chicago-based United on Thursday canceled 120 flights for Friday, while Atlanta-based Delta said it had canceled about 90. Both said they were working to contact passengers so they would not be stranded at airports.

Multiple airlines across the United States canceled hundreds of flights on Christmas eve, citing a nationwide surge in Omicron cases which has directly impacted employees and flight crew.

The cancellations come as more than 109 million Americans are expected to travel 50 miles or more via airplanes and other forms of transportation to visit friends and family over the festive period.

Passengers travelling home for Christmas have been hit with disruption worldwide after airline companies cancelled more than 3,000 flights on Friday, according to a flight tracking website.

The surge of Christmas Eve cancellations came as the rapidly spreading Omicron coronavirus variant meant carriers were unable to staff their flights.

Delta Air Lines is ditching a vaccine mandate for employees, according to company CEO Ed Bastian, who notably emphasized the “divisiveness” of such an order.

Bastian said announcing a plan to get all employees vaccinated, without enforcing a mandate, has worked, allowing the company to reach a 90% vaccination rate.

Unvaccinated Delta Air Lines employees who refuse to get inoculated against the coronavirus are going to pay the price.

Starting Nov. 1, unvaccinated employees on Delta’s account-based healthcare plan will get hit with a $200 monthly surcharge.  

It's a necessary policy, according to CEO Ed Bastian, who noted that the average hospital stay for COVID-19 costs the carrier about $50,000 per person. 

Rep. Rashida Tlaib was briefly detained by police Friday during a protest with airline workers at Detroit Metro Airport. The congresswoman was on hand to demand better pay and health care for the employees.

“We won’t stop until we get #fairwages & #healthcare. These courageous people got arrested tonight at DTW b/c they believe workers deserve human dignity,” the Michigan Democrat said in a tweeted statement, sharing a smiling photo of herself with protesters. “Shame on you @Delta for leaving workers behind and letting them live in poverty. @unitehere

Romulus — U.S. Rep. Rashida Tlaib joined airline catering workers who work for Delta Airlines on Friday to protest "poverty wages and unaffordable healthcare."

Tlaib locked arms with eight airline workers who sat blocking traffic at Detroit Metropolitan Airport while nearly 100 union members with Unite Here rallied outside Delta's McNamara Terminal departures. The protesters held signs reading "Delta: one job should be enough."

Refusing to move, eight airline workers were arrested by airport officers.