Delta and American Airlines have banned the shipment of big-game trophies on flights after the illegal killing of Cecil the lion in Zimbabwe.
The airlines announced that they would no longer transport lion, rhinoceros, leopard, elephant or buffalo remains.
They have not, however, given official reasons for their announcements.
Delta flies direct to a number of African cities and was subjected to an online petition to ban such shipments.
American Airlines flies to only eight sub-Saharan cities, far fewer than Delta, but said in a tweet its decision to stop carrying trophies was "effective immediately".
Cecil was shot illegally in July by US dentist Walter Palmer of Minnesota. Zimbabwe is seeking his extradition and that of a doctor from Pennsylvania, named as Jan Casimir Seski, who is suspected of killing a lion in April.
Mr Palmer is believed to have paid about $US50,000 to hunt Cecil, a major tourist attraction in the Hwange National Park.
He says he thought the hunt was legal and was unaware Cecil was protected, but the killing triggered a huge online backlash.
Delta would not answer questions from journalists as to why it made its decision on Monday, nor would it detail how many hunting trophies it has transported in recent years.
"Effective immediately, Delta will officially ban shipment of all lion, leopard, elephant, rhinoceros and buffalo trophies worldwide as freight," the company said in a brief statement.
Its announcement came as several other airlines indicated that they are - or soon will be - stopping the transport of all trophy-hunting kills.
As recently as May, Delta said it would continue to allow such shipments.