Sorry, last-minute holiday shoppers.

United Parcel Service Inc. and FedEx Corp. started capping air express deliveries in recent days after an 11th-hour increase in packages caused some retailers to exceed agreed-upon limits, according to people briefed on the situation.

This year, both UPS UPS, +0.87% and FedEx FDX, -1.66% held some retailers to their volume commitments during the final shopping days before Christmas, aiming to avoid a repeat of last year’s fiasco. Last Christmas, an estimated 2 million express packages didn’t arrive under the tree in time, according to software tracking developer Shipmatrix Inc.

Tom Barone, the vice president of North American operations for eBay Enterprise, which handles shipping and other logistical issues for close to 100 brands and retailers, said delivery companies had asked Tuesday for his clients to scale back last-minute shopping deals to take some pressure off shipment volumes.

Surging online shopping over the holidays fueled by offers of free shipping and deep discounts tests the limits of the infrastructure—planes, trucks and sorting hubs—used to deliver the gifts to tens of millions of homes in neighborhoods from Miami to Seattle.

Last year, UPS was caught flat footed by a surge in deliveries, a limited air fleet and bad weather and had to tell millions of Americans their gifts wouldn’t arrive in time for Christmas. FedEx said it wasn’t affected as badly, apparently because it rejected some last-minute unexpected volume, a demand UPS tried to meet, although it conceded it struggled with the weather.

An expanded version of this report appears at WSJ.com.