Let's say you're an Arcane Trickster Rogue, and you play in Adventurers League games. One night, you play at a DM's table, and during combat, when you would normally benefit from Sneak Attack, said DM tells you that you don't benefit from it, as "it would be too powerful with the magic given by the Arcane Trickster archetype".
Or let's say that you are a Small creature wielding a Lance, but the DM says that “you only deal 1d8 damage instead of 1d12 with it because of your size”.
These scenarios are only examples, but they share the idea of an AL DM blatantly altering existing rules. While it is generally seen as bad behavior to interrupt the game flow in order to point out something to the DM, are such situations (where the DM clearly alters the rules in a non-homebrew session) worthy of stepping up as a player at that moment ?
In other words, how should you react, as a player, when existing rules are modified by the DM in Adventurers League organized play (provided that you double-check beforehand that the rules were indeed altered)...
Point out the alteration immediately to the DM and politely ask him to stick to the rules -- but then if he refuses...
A) Accept it and do nothing
B) Go speak to the organizer (either now or at end of session)
Write it down to mention it to the DM during break time or at end of session (even if the rules alteration severely impacts the game at the moment)