If the average ping difference between two teams is more than 25, teams can open a Support Ticket under the type "League" to evaluate and potentially re-assign the match to a server with the most fair pings.
If a server is likely to be a poor choice both teams (for example Moscow for teams in Western Europe) then either team should make a ticket ahead of the match time to have it reassigned.
Teams may not dispute the server with a ping test if their geographical location is on the outskirts of a region resulting in the team always being able to play at a ping advantage. For example, if a team had some players living in far east Russia they could not force their opponent to always play in Moscow servers due to it having the lowest average but an overall abnormally high ping, relative to their other matches, for their opponents. However, teams are welcome to agree with one another to schedule on their preferred servers.