Sounds like they fear the outcome of a 99designs.com type world - and legitimately so. But, why wouldn't they just refuse to pitch to clients who do this? Alternatively, as they suggest, they should spend less on pitching - but my guess is that if the prize is big enough they'd do it anyway.
A strike seems like a silly response that could also be interpreted to attempting to reduce competition in a specific region and in effect form a cartel - a cartel that would seem to be counterintuitive especially when the barrier to good ideas is no longer limited within borders.
I have to wonder if "major players came together to design rules of the game" in the US in any industry group that it wouldn't be considered to be anti-trust.