Grain Train Inc. sells wheat to both Pack Inc. and Snack Inc., both manufacturers of wheat breads in New York. However, Grain Train Inc. helps Pack Inc. cut its costs by supplying wheat at low prices which in turn distorts the competition between Pack Inc. and Snack Inc. This is an example of a(n) _____ at the buyer's level.

bird abatement violation

resale price maintenance agreement

non-price horizontal restraint

secondary-line injury

non-price vertical restraint