I understand that companies get a lot of resumes these days, but the fact is that there are many, many much better ways of culling than to reject the unemployed. In point of fact, by stating up-front that you won't take resumes from those who aren't currently employed, you're cutting out what might be your best hiring pool. My experience is that people (myself included) who've been unemployed, especially for a little while, often have clearer heads going into a job, and tend to want it a whole lot more. Like I said, I was off the job recently for five months. You can take a guess as to how I attacked the work when I finally hit the job again: it was like I was living again. If I'd moved from my old job directly into the new, there would've been a longer adjustment period, I would've been more disoriented, and most importantly it would've taken longer to realign my motivation and ambition.
Being unemployed - being unable to provide for myself - focused me pretty sharply, I can tell you. And it made me eager to get back to work and dive into it. I think other people are the same; the until-recently unemployed can be some of the most motivated people on earth.
This is just to say, to anyone in a hiring position who's considering trying this to cut back on an abundance of resumes: increase the qualifications, streamline your resume review process, and even accept that you might have to pick a handful of resumes to work from at random - but don't throw away what might be the most motivated and willing pool of applicants available to you by asking for resumes only from people that are currently employed.