The air service is more expensive by about $25 per gun, but it's more secure, reports CBS News Correspondent Dan Raviv.
UPS spokesman Norman Black said the idea is to make it less likely guns will be stolen from the package system.
UPS handles as many as 75 percent of the guns sent from manufacturers to distributors and nearly 99 percent of firearms shipments from distributors to dealers, according to newspaper reports.
Rifles and shotguns, which are harder to conceal, will continue to be shipped by UPS' brown delivery vans.
Black said UPS is doing what a "socially responsible" company should do.