As far back as my short sales webcast, released almost a year ago, I’ve been telling Realtors that they do NOT have to agree to lower their commissions on short sales. Fannie Mae recently made this crystal clear with announcement 09-03, Miscellaneous Servicing Policy Changes, available as a PDF download on  eFannieMae.com.  From the document:

Servicing Guide, Part VII, Section 504.02: Contacting Selected Borrowers
Effective March 1, 2009, closing of preforeclosure sales may not be conditioned upon a
reduction of the total commission to be paid

Here’s the direct link to the PDF (18 KB).