ADDENDUM TO THE EARLIER POST: At this point, there are only two things to which Amazon is likely to respond: Governmental action on either the state or federal level, or negative consumer response.
The Federal Trade Commission stepped in ten years ago when Barnes & Noble tried to buy Ingram; ironically because such a purchase was likely to harm the then-infant Amazon. B&N had to back down.
I think it is a very real possibility that either the Washington State Attorney General or the FTC will look askance at Amazon's latest move.
However, the other more important influence is negative consumer response. The New York Times said in January that “Amazon has really had only one stated goal since it began: to be the most customer-centric company in the world.”
A consumer backlash will have the most immediate and lasting impact on Amazon.
Which is why I keep urging readers and writers to go here and sign that petition. I promise Amazon is listening.