Perhaps. However, that's not the same as taxes and its not a hidden cost like a tax. It's not factored into the price of US goods as US companies would use a private shipper if the this law significantly effected shipping costs.

At worst it hurts USPS revenue and increases the cost of first class mail as market forces can't compete for first class mail. My point is a lot of the comments are misleading about the scope of the costs involved here.