The introduction of Sunday delivery also benefits Amazon, enabling it to increase pressure on competitors, said Jason Long, a St. Louis-area retail consultant with Shift Marketing Group.

“It’s a big, big deal,” Long said. “I don’t think the Earth is going to shift. But it’s just another incremental loss for brick and mortar. And I think this just helps sustain the overall movement to online ordering.”

Members of Amazon’s popular Prime membership program can already get free delivery within two days. By adding Sunday delivery, those Prime members who might otherwise have gone to a store over the weekend if they needed an item for Sunday or Monday, may be more willing to order from Amazon in those instances.

“This will take out some of those trips to local brick-and-mortar retailers,” Long said.

And there is talk that Amazon could raise the prices for its Prime membership by $20 to $40. Right now, an annual membership is $79. Long noted that adding Sunday delivery might help blunt some of the outcries about the higher membership fees and might help deflect the fact that Amazon is now charging sales tax in many states where it is required to do so.