must be time for an election
I think the guy is bucking to win re-election, by getting some publicity. Clearly he didn't think it through, no one is going to want to pay a tax on tax (you are taxed on your monthly fees already). I don't know very many people that would spend a tax on each bit.
FYI, there are 8 bits in a Gigabyte. The lowest tax is either a penny per GB (.08 cents), or a percentage tax on total usage. Either of those options stinks. This would be like taxing gas, twice!
If the postal service can't stand on it's own, either lower the rates to increase usage of those services, or reduce costs to increase profits, both would be best. I'm sure there is a LOT of waste in the Postal Services with regards to inflated salaries and such above the street level delivery system.