Unless you work in shipping logistics or aviation, you’re probably not familiar with ABX Air. You can’t book a ticket on the Ohio-based airline; it doesn’t carry passengers. It carries boxes. And as the companies it carries boxes for — including Amazon — are ramping up for the super-busy holiday retail season, ABX pilots have gone on strike, potentially leaving a lot of those boxes in the lurch.

Roughly 250 pilots went on strike this morning, after voting back in May to approve a strike if it should become necessary later on.

The pilots union — represented under Teamsters Local 1224 — claims that the airline has been understaffed for nearly two years, representatives said in a statement. The union also claims that ABX refused to hire back previously furloughed pilots because they would have to be paid at the top of the wage scale, and instead hired an insufficient number of cheaper, newer pilots.

As a result, the union says, pilots are not being allowed to take comp time, as outlined in their contract, and they’re requiring pilots to work an excessive number of extra flights that they’re not scheduled for.

“To date in 2016, pilots have been scheduled to cover over 8000 emergency assignment days on days they should have had off,” the union writes. “As the airline moves into peak holiday flying season, ABX Air and ATSG are refusing to honor contractual provisions regarding compensatory time and vacation time in order to cover the pilot deficit.”

ABX says it will be seeking a court order later today to “restore the status quo operating environment” while discussions about “specific areas of concern” with union reps continue.

“We expect the court will uphold our position that the actions taken by the union to refuse work assignments is not legal, and the issues involved constitute a minor dispute to be resolved via arbitration under terms of our current labor agreements,” ABX Air President John Starkovich said in a statement.

He adds that ABX is notifying customers and other affected parties about the disruption in operations so they can adjust their networks until pilots return to work and normal flight operations resume.

“We stand ready to assist our customers in any way we can to minimize any impact on their own operations during this critical holiday period,” Starkovich said.

Earlier this year, Amazon purchased a 10% ownership stake in ATSG. The online giant had previously leased a fleet of 20 cargo planes from the company.

The strike may indeed post a problem for holiday shopping season. ABX flies 45 flights a day for DHL and another 35 a day for Amazon. With Christmas shopping already ramping up, and Black Friday and Cyber Monday on the very near horizon, consumers are set to start ordering items at a very high volume, and to expect them soon.

Unions at other cargo airlines, including Atlas Air, Southern Air, Kalitta Air, and Polar Air, have all vowed not to cross the ABX picket line. That means that if they’re asked to take on flights that ABX has had to cancel due to a lack of pilots, they won’t.

Pilots are picketing today outside ABX headquarters in Wilmington, Ohio and outside DHL’s North American hub at Cincinnati/Northern Kentucky International Airport, the union says.

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