"Accept this deal or else" is blackmail any way you want to cut it. Margarine, butter, or Tabasco - nothing will get rid of that taste.
I bought a bar of "butter" from the supermarket. The butter was racid. I told the guy at the supermarket, either accept an exchange of bad butter for good, else I want my money back.
A statement of "Accept this deal or else" is not synonymous with blackmail...in any way, shape or form.