You are asking for a big brother approach you realize. A top down government decree micro managing the entire hotel industry and ensuing bureaucracy. Why you ask?

Quite simply the first chain to raise prices and hit "you" in the pocket will see "you" going the the other hotel that does not have the laundry charge.

Also, all Cialdini's hotel towel example illustrates -if anything- is that patrons of upscale hotels can best be motivated to reuse towels if they are led to believe the majority of their guests are doing so.

Or it may not even illustrate that much. It might be possible, for example, that most guests who already reuse their towels do so for consciously environmental reasons. We would therefore not expect cards that carry a generic "save the environment" message to significantly increase towel reuse -these cards are targeted at an audience that has already bought into the message. The fourth card by contrast may appeal to people who don't care so much about the environment but do care about conforming to the apparent expectations of their peers. In that case the greater perceived efficacy of the fourth card is due to the fact it is in fact targeting a different audience, not because people are somehow predisposed to regard the way the message is framed more favorably.

It is worth noting in this regard that the first 3 cards contain only generic messages, while the fourth pairs the generic message with specific information that relates the guest's behavior to the desired outcome (which is in itself a potential methodological flaw).