Sometimes companies are just resistant to any regulation, and no matter what it is they just line up against it. In the United States they will be mandating this type of labelling for all restaurants. Some studies have demonstrated that the impact was very small in some neighbourhoods. But the real reason for objecting is because those companies essentially don't want to respond to informed consumer choice if they don't have to.
If you go to a restaurant, care about calories, and don't see anything you want to buy on the menu, you'll go to another restaurant. It's really about having informed choice, and they are often resistant to informed choice.