The auction by the Dallas Safari Club, part of the group's four-day convention, closes Saturday, but already may have drawn more potential protesters than bidders, the Dallas Morning News reported Thursday.
Angela Antonisse-Oxley, who is organizing a peaceful protest Saturday, charges the animal up for bids "is being hunted because he is old and unable to reproduce. It is barbaric to hunt and kill an animal merely for this reason."
A better option is to relocate the animal, she said, adding, "These animals need money, not bullets."
A Facebook page protesting the auction, the Black Rhino Rescue Project, has drawn 13,996 "likes" since being launched in November. Some 203 people have indicated they will be at the protest; 336 have clicked maybe.
Ben Carter, the club's executive director, rejects all the criticism.
"None of them had any scientific material. It's all emotional," he said.
On his side are major international conservation groups such as the World Wildlife Fund, the International Union for the Conservation of Species and the U.S. Fish and Wildlife Service, all of whom endorse the auction.
Namibia has auctioned permits to hunt black rhinos since 2004 with the nod from the Convention on International Trade in Endangered Species. During the period, the population of black rhinos has grown from 3,600 to 5,055.