You don't want to be submitted by two different recruiters for the same job. It's awkward for the job's HR and for everyone else involved, and could potentially invalidate your resume submission. But recruiting firms also use this mechanism to feel out their competition.

Rec: "I have a position with AAA Airline you might be interested in."

Me: :"Sorry I was already submitted to them via Firm B."

Rec: "Oh, you should have gone with us instead. It's always amusing watching them try to work the AAA Airline jobs. Are you working with SoAndSo?"

Me :"Yes..."

Rec :"ha ha ha, best of luck to you guy"

Ah, ok that makes sense. I wasn't really thinking about it from a recruiting firm's standpoint, but, you're right, that could cause problems.

This is only an issue for headhunters, not corporate recruiters. It's well within the right of corporate recruiters to ask this.