Recently some players have found a way to change the player limits on Operation Metro, allowing servers to let up to 128 players on it. Rock Paper Shotgun has spotted a DICE forum post, since removed, which stated that whoever enters these modded servers could have their Origin account suspended. That also means they could be denied access to the other games they have purchased through Origin.
Basically, even if you mis-click and enter a modded server, you run the risk of being banned and locked out of your Origin account. I can understand that EA and DICE want to keep server code nice and protected, but banning people who simply play on modded servers is not really a good way to bring on customers to the game.
We can only hope that the post may have been removed due to a revocation of these draconian rules.
The Battlefield 3 beta is ongoing, and the game is set for release on October 25th on the PC, PlayStation 3 and Xbox360.