Angry Amazon pilots are warning last-minute shoppers that holiday deliveries may be late

Amazon’s foray into controlling more of its air cargo shipments continues to be rocky.

On Friday, a Teamsters union representing cargo pilots who transport Amazon goods launched an online ad blitz aimed at educating Amazon customers on their working conditions. The ads, which were set to run on Facebook and Google, link to a site called “Can Amazon Deliver?” that outlines alleged staffing issues at two cargo airlines from which Amazon leases planes.

“Executives at the Prime Air contracted carriers ... overcommitted their operations by taking on Amazon’s business,” the website reads. “They took on the work despite known staffing problems, and the problems are getting worse.”

The site also warns Amazon customers that these staffing problems could lead to delayed deliveries.

“This holiday season, Amazon customers may want to think twice before ordering last-minute deliveries,” the site reads.

An Amazon spokesperson did not respond to a request for comment.

The ad campaign comes nine days after pilots for one of the airlines, ABX Air, were forced back to work by a judge after they had walked off the job over understaffing issues resulting in more than 8,000 emergency flights on what should have been off days for pilots.

Amazon had said it wouldn’t resume work with the airline until it was sure another strike wouldn’t happen. But a spokesperson for the pilots union told Recode on Friday that Amazon had started working with ABX again last weekend.

Still, pilots for ABX Air as well as another Amazon Prime Air partner, Atlas Air, are still looking to airline management to add more staff to ease workloads.

Earlier this year, Amazon inked deals with both companies to lease 40 planes over the next few years. Amazon has said its goal is to ensure that it has enough shipping room to meet growing demand from its customers, especially during the holidays when partners like UPS and FedEx may not be able to offer excess shipping capacity. The company also expects that taking control of more of its logistics operation can save it money over time.

Update: An Amazon spokesperson responded with a statement after publication: “Several weeks ago we rebalanced capacity across our network of carrier partners to ensure there are no disruptions through the busy holiday season, and this rebalancing remains in effect — we are confident in our ability to serve customers.”

This article originally appeared on Recode.net.