justification (§2(b) Robinson-Patman Act)

the key word 'justification' can be read no more broadly than to allow rebuttal of the respective offenses in one of the ways expressly made available by Congress. Thus, a discrimination in prices may be rebutted by a showing under any of the § 2(a) provisos, or under the § 2(b) proviso—all of which by their terms apply to price discriminations. On the other hand, the only escape Congress has provided for discriminations in services or facilities is the permission to meet competition as found in the § 2(b) proviso.