He is refering to the McCaskill/Bond law which went into effect a couple of years ago. Let me say though, you most certainly CAN staple a pilot group without their consent. The question that is usually asked is, "what are the job expectancy of the pilots?" "And would a staple be fair?" Some (not all) would argue that an airline in bankruptcy with your future being unemployment, a staple might be fair, with pay protections, domicile fence, ect ect ect.

This arguement would not work with a viable company. Now before I get flamed this is just one possible simplistic explanation of a possible staple. Not the end-all-be-all of arbitration or McCaskill/Bond law.