It can be sooo stressful and frustrating when a wedding task is almost complete, but you're just waiting on a bridesmaid or a groomsman or a parent or guest to send a check or a size card or just make a decision already! That one little response is the obstacle that's keeping you from getting the job done.

You've asked, you've reminded them, you've told them that the deadline is looming (or has passed) but they just won't deliver what you need. You're sitting at home stewing, almost hating that person right now, and wondering why they're keeping you hanging. We're not going to guess what their issue is right now. We're going to create that stern yet respectful e-mail that will light a fire under the straggler. Here's what you may wish to copy-and-paste in your missive to them:

"Dear (Name):

Just a reminder that your size card/deposit payment/travel info is due now, so that we can stay on schedule with the plans and prevent you from experiencing any hassles or rush fees. I know you're busy, but we really do need you to get this information to us by Wednesday at the latest. We can't put an order in until we have everyone's information, and we wouldn't want everyone to have to pay rush fees if we get the order in after deadline. So please make sure you get that info to me as soon as humanly possible. After this, there's very little to arrange for months, so I'm sure you're with me in wanting this task over, done with and off your plate! ;) Thanks for your understanding! And thanks for (the thing this person did well for you recently). With all the wedding details swirling, we're just trying to keep on top of things. See you soon!"

Notice you inserted a little positive reinforcement in there with the reminder that you appreciate what they did well for you, but you're showing the consequences of their delay (which included everyone else being angry at THEM for the delay.) You've also spelled out that they're not going to get hounded if they just fulfill a promise and that they have weeks of clear sailing after they get this one thing done. You've done all you can.

There's no need to threaten booting them from the wedding party. That doesn't motivate people, and in fact often slows them down further. If you want results, throw a bunch of positives in there.