The United States has told the World Trade Organisation that it would block the reappointment of one of the WTO's four remaining appeals judges next month, leaving the bare minimum of three on what is effectively the supreme court of trade.
There are normally seven members of the WTO's Appellate Body, but three have already left and Shree Baboo Chekitan Servansing needs to be reappointed for a second term next month.
Three judges is the minimum needed to hear appeals.
Trade diplomats and lawyers say the United States is precipitating a crisis at the WTO by vetoing judicial appointments.
A US official told the WTO's dispute settlement body on Monday that it was not in a position to agree to the reappointment, a Geneva trade official said.