Yes, but the onus would be on you to prove or at least demonstrate that it's true. In the meantime, Massive Company X will have great fun forcing you into the cost of solictors/barristers etc etc
But personal experiences are surely not grounds for libel/slander?
"I was treated like dirt by Company X, I wouldn't recommend you go anywhere near them. No-one got a bonus, the managers are very hard to work with and I'm glad I'll never darken their doors again"
I doubt your example would be Pique - but I'm certainly no expert.
Problem is, it wouldn't be too long before specifics start to come into it and I'd say that's where the danger lies - unless posters are very very careful about how they word things. And of course it would need to be 100% true.