the rules don't allow "Sheltering behind or taking advantage of the slipstream of a vehicle", no matter what kind of it is, or who is driving it.
The penalty for this always is "CHF 200 fine, 20%** penalty in the points and mountains classifications and/or 20 second to 5 minute penalty per infringement and 15 points from UCI rankings" for the rider and "CHF 500 fine" for the driver, as it was applied yesterday:
Additionally it says in the rules, "in serious cases, in cases of repeated infringement or aggravating circumstances or if an infringement offers an advantage, the Commissaires’ Panel may eliminate or disqualify a rider and/or exclude a licence holder" - but this did not happen yesterday.