In Pittsburgh v Lanese, the issue was delegating the taxing powers to 3rd party collectors. It clearly states in the Constitution that delegating any government function is prohibited. The ruling sided with the theory of Tax Collection is administrative not a sovereign power. Yet other cases when contesting the fees applied to the tax bill, it was determined to be part of the taxes.

The collection penalty "is inexorably tied to the tax collection itself, which sustains the essential flow of revenue to the government." Id., 338 F.3d at 444 

A plain definition to levy tax is to impose a heavy demand.  Portnoff law firm creates a face amount that is the tax amount, penalty, notice fee and 5% for the tax claim bureau.  From this sum they collect interest.  Also adding attorney fees and costs.  This doubles, even triples the original amount.  They change the amount levied by the government and it imposes a heavy financial demand.