This is from the dispute settlement chapter of USMCA (Inu pointed it out to me):
Article 31.9: Panel Composition
...
3. A panelist shall normally be selected from the roster. A disputing Party may exercise a peremptory challenge against an individual not on the roster who is proposed as a panelist by a disputing Party within 15 days after the individual has been proposed, unless no qualified and available individual on the roster possesses necessary specialized expertise, including as required by Article 31.8.3 (Roster and Qualifications of Panelists), in which case a disputing Party may not exercise a peremptory challenge but may raise concerns that the panelist does not meet the requirements of Article 31.8.2 (Roster and Qualifications of Panelists).
This provision looks like it was changed significantly during the legal scrub from the originally released USMCA version, which had simply been carried over from the original NAFTA.
But what does the added language mean? Specifically, what is the role of peremptory challenges where the parties have not yet agreed on a roster?
I can see an argument that the absence of a roster means there are no "qualified and available individuals on the roster" possessing the "necessary specialized expertise," which means peremptory challenges may not be used. Under this interpretation, in the absence of a roster, it may be possible to get a panel appointed because no one can use the peremptory challenges that caused a problem in the original NAFTA.
On the other hand, I can also see an argument that the exclusion on the use of peremptory challenges only applies where a roster is actually in place, and that without a roster in place peremptory challenges can be used. Under this interpretation, where there is no roster in place, peremptory challenges could be used to block the appointment of a panel just like under the original NAFTA.
And here's another question: Who gets to decide if an individual on the roster "possesses necessary specialized expertise"?
