ARRL's page about it.
The intention is to create essentially a nationwide emergency WiFi. Seems to me to be redundant because most established public safety already have data services and so why would they want to add another network? They are already moving to standardize on spectrum in the 800MHz band anyway.
BTW, it's not just hams who are worried, there is 700MHz spectrum being reallocated. It's moving some VHF public service up to UHF.
Be sure to write your Congressman to oppose it. Not that it will matter, the spectrum is too valuable in auction to allow us to keep using for 'free'.