If it's because of a family emergency, a $$ emergency (i.e. lost your loan or scholarship or source of funding for whatever reason) or if you just found out you need to take 10 additional credits or something, the fraternity probably would be OK with you finishing your pledging next semester.
But if you just aren't feeling pledging this semester, then they might tell you to go jump in the lake.
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It is all 33girl's fault. ~DrPhil