[33girl]

Sororities can bid as many upperclassmen as they want. If they want to take an entire pledge class full of seniors, that's their business. There are absolutely no written rules dictating what class status new members must have, although sororities often prefer to bid freshmen as they'll be around longer. What you are more likely referring to is "free" juniors and seniors - the sororities are allowed take a certain amount of juniors and seniors and it doesn't count against quota.