Just about every other major studio is doing it, and Disney appears on the verge of requiring a 28-day waiting period before new releases from the studio are made available on Netflix. Warner Brothers, Universal, and Fox all already have at least a 4-week waiting period.
Disney held an investor call this week and discussed the possibility of imposing the waiting period to protect the initial window of DVD and Blu-ray new release sales.
While Disney is only considering the move at this point, there have been no mentions of when the move could become official. It's likely that a move would not only affect Netflix, but other rental services like Redbox.