Southwest Airlines is now apologizing after a chaotic week of canceling thousands of flights.

“There’s a lot to say about what happened over the last several days, but we’ll start with the most important message: we’re sorry,” the airline stated on Twitter. “Cancelling thousands of flights and displacing customers isn’t what we want for you, nor is it what you should expect from us.”

Tens of thousands of passengers were left stranded from the weekend into Monday amid the airline’s latest round of flight cancellations and delays.

The airline canceled more than 380 flights and delayed more than 1,456, according to the online flight tracker FlightAware. Southwest’s canceled flights made up 10% of its schedule on Monday and 30% on Sunday.

In a statement, Southwest says the weekend delays were “primarily created by weather and other external constraints, which left aircraft and crews out of pre-planned positions to operate our schedule on Saturday. Unfortunately, the out-of-place aircraft and continued strain on our crew resources created additional cancelations across our point-to-point network that cascaded throughout the weekend and into Monday.”

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The airline stated on Oct. 11 that it was “working diligently to restore stability to the network […] and we hope to restore our full schedule as soon as possible.”

A spokesperson added the delays and cancellations had nothing to do with “operational challenges regarding employee demonstrations” as several reports have speculated flight crews are protesting company policies. The airline recently announced a vaccine requirement for all its employees by Dec. 8. Without the vaccine, Southwest employees risk losing their jobs.

“Southwest Airlines must join our industry peers in complying with the federal government’s COVID-19 vaccination directive,” said Gary Kelly, Southwest Airlines chairman, and chief executive. “I encourage all Southwest employees to meet the federal directive, as quickly as possible, since we value every individual and want to ensure job security for all.”

Southwest has especially struggled throughout the pandemic as more people feel comfortable traveling again. In June, the airline experienced a system-wide outage that caused massive delays and cancellations for two days throughout the country.

The airline also warned in August that the cancellations were on the rise because the Delta variant complicated travel.

Related: Nationwide Flight Cancellations: What’s Causing Them?