So Verizon was definitely being sketchy and should pay everything they owe.
However, the description of the bill is making me a bit leery. As described, wouldn't this be an ex post facto law? Which the US in general has historically frowned on (for good reasons).
Isn't the bill just saying "you always owed these taxes," though? It's not adding a new tax.
It's saying "you always owed these taxes" by revising the existing law retroactively.
That's the definition of ex post facto.
As I read the story, the current law codifies the intent of the prior law to explicitly say that Verizon's interpretation of the original law was incorrect, and to re-affirm that this is not an annual threshold. Once you meet that threshold, you owe the taxes henceforward.
Verizon may have a case if they can support their interpretation of the original law with facts showing they simply didn't meet the criteria; that they apparently chose to understate their actual market share at least in some communities in what *could* be painted as tax fraud probably doesn't help that case.