I'm not a lawyer, nor will I ever pretend to be one. But where in the letter does it say they can't advertise a markup fee at all? To me, the letter sounds as if some dealers are slapping on the fee after they've already gotten the customer hooked in on a car. Then...
"oh yeah, it's actually $5k above that because you know, all the dealers are doing it. Some are doing $10k to $15k!" That should be outlawed, for sure. Much like the cases where it's significantly more than just $15k over MSRP - like 50% or 75% of the car is "Market Adjustment Fee's". Those are the ones that I suspect GM is really going after in this letter.
However, if the Dealers are upfront and saying they're going to charge $x above MSRP within 10% of MSRP, then what's unethical about that? I agree with Bill - it's supply and demand. When there isn't enough to go around, then those that are willing to pay more are going to get it b/c that's the way the world turns. I don't like it, but it's truth and definitely a grey area for sure.
I also have to think that when the market returns to a better state - would you be willing to sacrifice the "less than MSRP" you would have gotten in years before, so that the Dealers would charge exactly MSRP? I doubt it. I also doubt that GM has any legal right to go after any of the Dealers doing the dirtiest of dirty practices, too. At best, they shift allocation from A to B. Dealers are slimey, no matter what and will always get their coin. Maybe Tesla model is really onto something?
OK - it's late. I'll get off my soapbox. Feel free to tear me apart LOL