Tax discrimination against people with low and middle incomes is blatant in the US today.  It is assured by the ability of corporations and the wealthy to make disproportionate campaign contributions.  It is exacerbated by the fact that the Members of our Congress themselves are wealthy and have high incomes. 
Until recently, our major representational problem in Congress was that there were very few members who understood at first hand the needs, wishes, problems and aspirations of our various minority groups. We have made some progress toward solving this problem. However, we have made no progress at all toward providing representaion for the majority of Americans. Like Shays and his army of farmers and artesians, our middle and lower income and wealth groups are not represented in the body that determines their taxes.
It is in the economic interest of the Members of Congress to tax ordinary Americans heavily and wealthy and high income Americans lightly. One-half of the Members of Congress are millionaires. Their congressional pay alone puts the remaining half in the upper 10% of Americans. We accept this over- representation of the upper ten percent with hardly a murmur. Yet there can be little doubt but what it contributes heavily to the US having the most extreme income gap in the developed world. See Chap. 7 of my recent book Reversing America's Decline: Jefferson's Remedy for tables showing US world rankings in the quality of life.
This lack of representation, when considered along with the ability of wealthy individuals and corporations to make disproportionate campaign contributions, presents our democracy with a serious problem. We can resolve this two-pronged problem only by altering our Constitution so as to make our government more responsive to the needs of the lower ninety percent of Americans. This means petitioning our state legislatures to apply for a 2nd constitutional convention made up of delegates elected without the benefit of private campaign contributions. This could lead to a number of key reforms, including term limits and the exclusion of private money from all federal election campaigns.
I am indebted to "Shays' Rebellion" in West's Encyclopedia of American Law for much of this factual information .
 J. E. Stiglitz wrote, in the Apr. 14, 2013 New York Times, ("A tax system stacked against the 99 per cent"), that the share of income going to the top 1% has doubled since 1970."
 See Citizens United v. the FEC (2010)
 Eric Lipton, "Half of congressional members are millionaires," New York Times, Jan. 9, 2014. According to a Congressional Research Service report dated Jan. 7, 2014; most Members of Congress are paid $174,000 per year.