You're assuming votes are public, which is not usually the case. If there's no way to check someone else's vote, there's no way to enforce a voting block.
If you can see the ballots, you can filter for the ones that match the cartel platform, and count to 100. There may be a voting coordination strategy to find out who cheated. Maybe instead of 100 members, you have 99, and each member votes 2 for a different issue.