Level 7 Referee
This was announced over the weekend. The release is confusing, but the general consensus on a different referee forum is that MLS will have new kits from Capelli Sports starting with the 2021 season. PRO handles assignments for MLS, NWSL (top-flight women's league), and USL (lower professional and high-amateur leagues), but many USL and NWSL crews have a local referee (or referees) who are not necessarily part of the PRO referee cohort. Capelli is a US-based organization with a decent-sized footprint in the youth and lower amateur/professional levels in the United States. All MLS teams have Adidas kit because the Adidas deal is with the league instead of clubs, so I was a bit surprised that this deal was able to take precedence over the Adidas deal for kits and game balls to be Adidas.
The only Capelli kit I've seen from their team catalog likely won't be what's worn by the MLS officials since they are, quite honestly, pretty ugly. I won't even show the "in action" photo as it showed the referee with a neck lanyard like a basketball referee . . .