Even a budget airline has responsibilities to its passengers that go beyond the legal jargon in fine print, as Sun Country has now discovered.

In an outrageous abdication of that basic obligation, Sun Country left 250 of its Minnesota-bound passengers stranded in Mexico last weekend. The airline’s wholly inadequate excuse? It was the end of its vacation season. When a historic April blizzard socked Minneapolis-St. Paul International Airport, airline officials announced that the canceled flights were the last it had scheduled to fly from Mexico this season. Instead of helping passengers rebook, Sun Country initially said it would refund just the return portion of the fares and left many passengers to fend for themselves in securing that costliest of travel commodities — a last-minute flight.

The airline finally appeared to come to its corporate senses Tuesday, announcing that it would reimburse passengers for all “reasonable” costs they incurred after the return flights were canceled, but that was only after the company created its own public relations fiasco.

Americans have put up with a lot — a LOT — from airlines in the name of deregulation and lower fares. Conditions at one point had so deteriorated that Congress passed a “passenger bill of rights” stating that airlines could no longer force travelers to stay on a grounded plane for more than three hours without food, water or the ability to disembark. Think about that.

As it turns out, that wasn’t nearly enough. As part of its Contract of Carriage language, Sun Country includes this astonishing sentence: Purchase of a ticket does not guarantee transportation. What on earth, then, are passengers purchasing? It’s understood that a budget airline may lack the niceties of a major carrier. There may be additional fees. The seats may be a little more cramped. But no way home? That’s too much.

Fortunately, Minnesota’s two U.S. senators agree. In a stern letter to Sun Country CEO Jude Bricker, Sens. Amy Klobuchar and Tina Smith stated that “after canceling flights, airlines have an obligation to support consumers who are making short-notice international travel plans.” They were seeking additional information about how the airline handles such situations.

Marty Davis, former Sun Country board chairman, told an editorial writer Tuesday that “nothing justifies leaving the customer there. It’s very unfortunate.” He also said operations had not changed materially since a recent sale to new owners. “If mistakes were made, they were made within the ecosystem we operated in prior to the sale, and they will get fixed,” he said. Soon after, Sun Country announced it would reimburse customers for their extra expenses.

That’s the right thing to do. But in the meantime, Sun Country has done incalculable damage to its relationship with its customers. That trust must be rebuilt, and the best way would be with a pledge that a return ticket is an obligation the airline intends to honor.