Abusing the system implies that only if Walmart stops doing the abuse, somehow abuse will stop, but this clearly is not the case.
Contrary to what writers of this article believe, prices are not formed in isolation of buyer and seller, in this case labor is being sold, and if Walmart does not lower the salaries and transfer the savings to the customers then some other company is going to beat the to it and manage to provide the cheapest good for the same quality.
Most people believe that when a company does something X, to achieve a reduction in costs, then it simply uses it to increase it's own profit margin, but they don't understand that instead of increasing their current profit margin, they can increase their future profit margin by selling their products for less by passing that lower cost to the customer.
Calling it a 'Walmart' tax is a spin on things which is aimed to invoke emotional imagery, it's like if NJ lawmakers called a tax as 'Tesla tax' because by bypassing the dealers they are putting more people out of job and on welfare, therefore the tax which will be used increase the benefits is 'Tesla Tax'.
There is a wide welfare structure in America, and the market will reflect that. If you give certain group of people free healthcare, then their employers will stop providing them with healthcare, if they give 3% 401K contribution to all working employees then yes, their employer's contribution will go down by 3%.