The free market makes it such that they can go work somewhere else if they dont think the grocery store is paying them what they are worth.
How would you like it if you went to that grocery store and they were selling a dozen eggs for $500 - and you were forced to buy them ? You go into that store and if you think that are asking to much for something you go elsewhere to buy it or you dont buy it at all.
It is a free market system. The grocery store offers whatever it is that they offer, and the workers will either say yes or no. If the workers think they can get a better deal in a different workplace, then more power to them. They have that right.
You have the right to not cross the picket lines, but we also have the right to decide for ourselves whether or not we will. I would cross it without hesitation. The workers have many weapons at their disposal ( finding a better job, going to college and getting something better, advancing into management, etc. ). These workers are not being forced to work in these stores like slaves. They have choices.
What it comes down to is that most workers want to work an easy job that doesnt require much from them, but when payday rolls around they want to be paid like Bill Gates.