On what basis can the US Supremes overturn this clause?

The Dormant Commerce Clause, or Negative Commerce Clause, in American constitutional law, is a legal doctrine that courts in the United States have inferred from the Commerce Clause in Article I of the US Constitution. The Commerce Clause expressly grants Congress the power "[t]o regulate Commerce with foreign Nations, and among the several States, and with the Indian Tribes." The concept of the Dormant Commerce Clause is that if a statute passed by Congress is silent on a point of interstate or international commerce, states are free to pass legislation that might pertain to it if the state law does not discriminate against or inappropriately burden interstate commerce. The restriction is self-executing and applies even in the absence of a conflict between state and federal statutes, but Congress may allow states to pass legislation that might otherwise be forbidden by the Dormant Commerce Clause.^[1]

This clause says that if I order an item from New York,and the US Post Office delivers it to me, then California cannot make the New York firm collect a local sales tax. 

The Supremes are going to make shit up and overturn this clause, full Sotomayor. The idea is that Amazon will become our universal sales tax collector, and Jeff will charge the states a fee for doing this service.  Meanwhile he get yet another transportation subsidy paid for by little brown taxpayer. This is one of the total mis-coordination rulings, like the Citizens United nightmare. This should be a transportation tax, not a local sales tax. 

So, we end up shifting taxes from the transportation department to city services, this adds a permanent wedge in commerce. The states will engage in anti-global warming, and the environmentalists will be proud.  Mis-taxing is the reason the Commerce Clause was written.