I have a genuine knack for allowing myself to be sucked into the most obscure and generally useless backwaters of the legal word, by accident. But since it was so damn difficult for me to even begin to get a grip on the issue, I have to share what I found.
The Home Affordable Foreclosure Alternatives (HAFA) is a U.S. Treasury program which arose from the recent (2007 - 2009) global economic and real estate bad dream. Part of the program provides Federal subsidies to mortgage lenders to encourage short sales for borrowers in financial distress. As part of the HAFA program, residents of the properties which are subject of the short sales (whether owner occupant or rental tenants) are required to vacate the premises when the short sale closes.
Since there are Federal subsidies involved, the mortgage lenders must be in compliance with the requirements of the Uniform Relocation Assistance and Real Property Acquisition Policies Act of 1970 (42 USC § 4601, et seq.), in general, and specifically, the provisions for resident relocation assistance, found at 42 USC § 4621, et seq.
If you are looking to understand relocation assistance under HAFA, these Code sections and any relevant Treasury Department regulations are the place to look.
I hope that helps.