There was a time in the not-so-distant past when the question of matching bridesmaid hairstyles would have been a really silly one. Check out any wedding album from the beginning of time through the 1980s or so, and you'll find page after page of bridesmaids in matching dresses with matching bouffants and French twists. Bridesmaids served one purpose and one purpose only: to present a unified front for the all-important formal photos.
But if you've been to a wedding in the past decade or so, you know that things are changing. The trend now is definitely away from the unified-front look -- plenty of brides still choose matching dresses for their bridesmaids, of course, but it's becoming more common to let bridesmaids pick different dress styles in the same color, for example.
These days, if everything's exactly the same down to the shoes and nail polish, you run the risk of looking dated.
The same goes for hair. Your bridesmaids have already bought a dress of your choosing, and they'd probably appreciate the chance to go with a flattering hairstyle instead of a one-size-fits-all 'do. There are plenty of ways to keep a consistent look for the group without forcing the same style on everyone. You can certainly make suggestions or set limits -- a general "put it up" or "leave it down" is often sufficient -- or you could give everyone the same clip or flower to put in their hair.
That said, if your wedding vision is 11 bridesmaids in identical midnight satin dresses with identical side-swept chignons, so be it. You obviously have every right to fulfill your dreams. But you need to go about it in the right way to avoid a style disaster -- or a bridesmaid revolt.
Just remember that you need to make the request in the most thoughtful, non-bridezilla way possible. Get input from the group, and make sure everyone's on board with the style you choose. And make sure the 'do works with the dress -- if it doesn't, the mistake is going to be magnified 11 times. If the bridesmaids' dresses are elaborately ruffled one-shoulder ball gowns, don't insist on a complicated hairstyle. Keep it simple.
And, above all, if you insist on matching hairstyles, make your bridesmaids happy by paying for the hairstylist!