Visa charges an Acquirer Processing Fee (APF) of $0.0195 per transaction. Mastercard charges a Network Access and Brand Usage (NABU) fee of $0.0195 per transaction. Discover charges a similar Network Authorization Fee. These are tiny, but they apply to every authorization — including declines — so high-decline merchants feel them more.
Like interchange and assessments, network access fees are non-negotiable wholesale costs. Every processor pays them; they appear either itemized (on interchange-plus) or rolled into the bundle (on flat-rate).