So why is this? Manufacturers *cannot* set actual selling prices, per
federal law (Sherman Act and related) so it is strange that they try to
impose this barrier.
That's exactly why they have the concept! (It wasn't the Sherman act.
Minimum retail price fixing was stilll very much around when I was in
high school, and I post-date the Sherman act

Basically they're
saying: I can't stop you from selling cheaper, but I damn well can
stop you from boasting about it.
Think of all the merchants who promise to meet any competitor's
"advertised price". You're supposed to bring in a clipping to show
them, and they'll rebate you the difference. Presumably they wouldn't
honor an email, since that was a private offer just to you.
all the best -- Dan Ford
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