A rhino breeder in South Africa has opened an online auction of 264 rhino horns that has raised alarm among leading conservation groups that fear a legal domestic trade could encourage more poaching.

The auction website indicates that bidding began Wednesday and will end on Friday.

Breeder John Hume says a legal trade in rhino horn will undercut poaching that has occurred at record levels in past years. But critics believe it will spur demand and tempt poachers to launder rhino horns into the legal trade.

A South African court ruling opened the way to a domestic trade in rhino horn, though South Africa says it remains party to an international ban in place since 1977.