What are the FAA/CS requirements for rubber chocks?
I could not find FAA requirements; however, there is an industry standard: SAE J348 (the details are behind a paywall).

A 1993 flightsafety.org publication emphasizes that chock placement and design are essential, for example:


  The chock’s height is very important and it depends on the size of wheel to be restrained. For heavy transport aircraft, a six-inch (15.2 cm) height for wooden or rubber chocks is effective in general ramp usage. For restraining an aircraft during ground run-up operations, most operators use larger, fabricated steel chocks of greater height, sometimes as much as 12 or 15 inches (30.5 or 38.1 cm).