Are the networks still allowed to call states before polls close?

[Starbucks Union Thug HokeyPuck]

I was wondering how this might affect the upcoming election, because it may have in 2000.  

Florida for example.  It was called for Gore 30 minutes before the last polls in the panhandle closed.  This could disenfranchise voters because they'll assume its already decided and there's no point in voting.  MI, NH, and TN, are all potential swing states and have 2 poll closing times.  Has there been any rule made that says you have to wait until ALL the polls in the states are closed?  

If not I hope they get on that pretty soon.