When I was there in the first decade of this century, exactly that happened in a downturn. Major oilco said "we're tearing up the contract, what are you going to do about it - sue us ?"
All I can say is that it’s very unethical to act like that and although I have been in some very uncomfortable meetings on both sides of the business, when in the oil company side, remedies due to any service issues had to be applied strictly contractually. I would have been fired for threatening a contractor.
I have also seen helicopter companies say “no” to something commercially disadvantageous. I accept though that the relationship can appear unequal at times.